Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	$ (33,622)	$ (33,622)	$ (3,145)	$ (4,203)
Unrealized (loss) gain on SERP, net of tax effect of $138, $24, and $(79), respectively	(412)	(77)	264
Beginning balance	(33,622)	(3,145)	(4,695)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	61,006	(35,192)	2,994
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2,376)	5,773	(1,444)
Net other comprehensive income (loss)	58,630	(29,419)	1,550
Ending balance	25,008	(33,622)	(3,145)
Unrealized holding gains (losses) on AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	21,399	(47,591)	(10,026)	(12,556)
Beginning balance	(47,591)	(10,026)	(14,916)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	71,222	(40,808)	6,334
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2,232)	5,773	(1,444)
Net other comprehensive income (loss)	68,990	(35,035)	4,890
Ending balance	21,399	(47,591)	(10,026)
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	3,629	13,433	6,352	7,740
Beginning balance	13,433	6,352	9,956
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(9,804)	5,693	(3,604)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0
Net other comprehensive income (loss)	(9,804)	5,693	(3,604)
Ending balance	3,629	13,433	6,352
Impairment loss on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	0	144	144	144
Beginning balance	144	144	144
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(144)	0	0
Net other comprehensive income (loss)	(144)	0	0
Ending balance	0	144	144
Supplemental Employee Retirement Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	(20)	392	385	$ 469
Beginning balance	392	385	121
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(412)	(77)	264
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0
Net other comprehensive income (loss)	(412)	(77)	264
Ending balance	$ (20)	$ 392	$ 385