Comprehensive Income - Summary of Changes in Components of Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 725,263	$ 623,739
Other comprehensive income (loss) before classifications	6,947	4,149
Amounts reclassified from accumulated other comprehensive income	(254)	0
Other comprehensive income	6,693	4,149
Balance at end of period	736,922	681,343
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	1,936	(8,782)
Other comprehensive income (loss) before classifications	7,284	4,363
Amounts reclassified from accumulated other comprehensive income	(254)	0
Other comprehensive income	7,030	4,363
Balance at end of period	8,966	(4,419)
Unrealized Gains (Losses) on Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	317	903
Other comprehensive income (loss) before classifications	(337)	(214)
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	(337)	(214)
Balance at end of period	(20)	689
Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(5)	41
Other comprehensive income (loss) before classifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	0	0
Balance at end of period	(5)	41
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	2,248	(7,838)
Other comprehensive income	6,693	4,149
Balance at end of period	$ 8,941	$ (3,689)