Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Total available for sale, Fair Value	$ 400,748	$ 212,420
State and Municipal Obligations
Assets:
Total available for sale, Fair Value	35,270	132,142
Residential Mortgage-backed Securities
Assets:
Total available for sale, Fair Value	321,611	43,093
U.S. Treasuries
Assets:
Total available for sale, Fair Value		37,185
Level 2
Assets:
Total available for sale, Fair Value	400,748	212,420
Fair Value Measurements on Recurring Basis \| State and Municipal Obligations
Assets:
Total available for sale, Fair Value	35,270	37,185
Fair Value Measurements on Recurring Basis \| Residential Mortgage-backed Securities
Assets:
Total available for sale, Fair Value	321,611	132,142
Fair Value Measurements on Recurring Basis \| Equity Securities at Fair Value
Assets:
Total available for sale, Fair Value	23,665	24,000
Fair Value Measurements on Recurring Basis \| SBA Servicing Rights
Assets:
Total available for sale, Fair Value	2,244	2,953
Fair Value Measurements on Recurring Basis \| Customer Interest Rate Swaps
Assets:
Total available for sale, Fair Value	1,401	3,009
Fair Value Measurements on Recurring Basis \| Correspondent Interest Rate Swaps
Liabilities:
Total available for sale, Fair Value	(1,401)	(3,009)
Fair Value Measurements on Recurring Basis \| Cash Flow Hedge Swap
Assets:
Total available for sale, Fair Value	1,728
Fair Value Measurements on Recurring Basis \| Corporate Bonds
Assets:
Total available for sale, Fair Value	43,867	43,093
Fair Value Measurements on Recurring Basis \| Level 1 \| Equity Securities at Fair Value
Assets:
Total available for sale, Fair Value	23,665	24,000
Fair Value Measurements on Recurring Basis \| Level 2 \| State and Municipal Obligations
Assets:
Total available for sale, Fair Value	35,270	37,185
Fair Value Measurements on Recurring Basis \| Level 2 \| Residential Mortgage-backed Securities
Assets:
Total available for sale, Fair Value	321,611	132,142
Fair Value Measurements on Recurring Basis \| Level 2 \| Customer Interest Rate Swaps
Assets:
Total available for sale, Fair Value	1,401	3,009
Fair Value Measurements on Recurring Basis \| Level 2 \| Correspondent Interest Rate Swaps
Liabilities:
Total available for sale, Fair Value	(1,401)	(3,009)
Fair Value Measurements on Recurring Basis \| Level 2 \| Cash Flow Hedge Swap
Assets:
Total available for sale, Fair Value	1,728
Fair Value Measurements on Recurring Basis \| Level 2 \| Corporate Bonds
Assets:
Total available for sale, Fair Value	43,867	43,093
Fair Value Measurements on Recurring Basis \| Level 3 \| SBA Servicing Rights
Assets:
Total available for sale, Fair Value	$ 2,244	$ 2,953

Spirit of Texas Bancshares, Inc. 10-K