Investment Securities Available for Sale - Fair Value of Available for Sale Securities and Related Gross Unrealized Gains and Losses Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,054,744	$ 1,856,026
Gross Unrealized Gains	83,702	32,150
Gross Unrealized Losses	4	1,452
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	2,138,442	1,886,724
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,711,738	1,742,221
Gross Unrealized Gains	76,108	26,403
Gross Unrealized Losses	0	1,382
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	1,787,846	1,767,242
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	100,001
Gross Unrealized Gains	0
Gross Unrealized Losses	4
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	99,997
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	90,162	88,301
Gross Unrealized Gains	6,721	5,594
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	96,883	93,895
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,504	5,504
Gross Unrealized Gains	253	153
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	5,757	5,657
Obligations of U.S. Government Sponsored Entities and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	147,339	20,000
Gross Unrealized Gains	620	0
Gross Unrealized Losses	0	70
Allowance for Credit Losses	0
Available for sale debt securities, at fair value	$ 147,959	$ 19,930

CenterState Bank Corp 10-Q