Comprehensive Income - Summary of Changes in Components of Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 763,784	$ 725,263
Other comprehensive (loss) income before classifications	(13,088)	6,947
Amounts reclassified from accumulated other comprehensive income	0	(254)
Other comprehensive income, net of tax	(13,088)	6,693
Balance at end of period	768,065	736,922
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	11,397	2,248
Other comprehensive income, net of tax	(13,088)	6,693
Balance at end of period	(1,691)	8,941
Net unrealized gains (losses) on available for sale securities:
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	11,402	1,936
Other comprehensive (loss) income before classifications	(13,135)	7,284
Amounts reclassified from accumulated other comprehensive income	0	(254)
Other comprehensive income, net of tax	(13,135)	7,030
Balance at end of period	(1,733)	8,966
Unrealized gains (losses) on derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	25	317
Other comprehensive (loss) income before classifications	47	(337)
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income, net of tax	47	(337)
Balance at end of period	72	(20)
Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(30)	(5)
Other comprehensive (loss) income before classifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income, net of tax	0	0
Balance at end of period	$ (30)	$ (5)