Fair Value Measurements and Fair Values of Financial Instruments - Summary of Estimated Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair Value	$ 35,798	$ 52,373
Held to Maturity, Fair Value	19,231	19,665
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	30,495	8,257
Fair Value	36,371	52,373
Held to Maturity, Fair Value	18,548	18,665
Loans receivable, net	514,847	515,522
Restricted stock	2,032	1,416
Accrued interest receivable	1,896	2,007
Deposits	511,986	523,150
Subordinated debt	9,238	9,231
Accrued interest payable	841	844
Portion at Fair Value Measurement [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	30,495	8,257
Fair Value	35,798	52,373
Held to Maturity, Fair Value	19,231	19,665
Loans receivable, net	516,353	519,721
Restricted stock	2,032	1,416
Accrued interest receivable	1,896	2,007
Deposits	509,908	521,922
Subordinated debt	9,386	9,539
Accrued interest payable	841	844
Portion at Fair Value Measurement [Member] \| (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	30,495	8,257
Fair Value		35
Portion at Fair Value Measurement [Member] \| (Level 2) Significant Other Observable Inputs [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair Value	35,798	52,338
Held to Maturity, Fair Value	19,231	19,665
Restricted stock	2,032	1,416
Accrued interest receivable	1,896	2,007
Deposits	509,908	521,922
Subordinated debt	9,386	9,539
Accrued interest payable	841	844
Portion at Fair Value Measurement [Member] \| (Level 3) Significant Unobservable Inputs [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Loans receivable, net	516,353	519,721
Federal Home Loan Bank of Pittsburgh advances [Member] \| Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Federal Home Loan Bank of Pittsburgh advances	40,025	24,625
Federal Home Loan Bank of Pittsburgh advances [Member] \| Portion at Fair Value Measurement [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Federal Home Loan Bank of Pittsburgh advances	39,909	24,546
Federal Home Loan Bank of Pittsburgh advances [Member] \| Portion at Fair Value Measurement [Member] \| (Level 2) Significant Other Observable Inputs [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Federal Home Loan Bank of Pittsburgh advances	$ 39,909	$ 24,546

FIRST PRIORITY FINANCIAL CORP. 10-Q