Comprehensive Income - Summary of Changes in Components of Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 736,922	$ 681,343	$ 725,263	$ 623,739
Other comprehensive income (loss) before classifications			9,423	9,646
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			(254)	0
Other comprehensive income	2,476	5,497	9,169	9,646
Balance at end of period	745,489	698,463	745,489	698,463
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	8,941	(3,689)	2,248	(7,838)
Other comprehensive income	2,476	5,497	9,169	9,646
Balance at end of period	11,417	1,808	11,417	1,808
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	8,966	(4,419)	1,936	(8,782)
Other comprehensive income (loss) before classifications			9,796	10,139
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			(254)	0
Other comprehensive income	2,512	5,776	9,542	10,139
Balance at end of period	11,478	1,357	11,478	1,357
Unrealized Gains (Losses) on Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(20)	689	317	903
Other comprehensive income (loss) before classifications			(373)	(493)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			0	0
Other comprehensive income	(36)	(279)	(373)	(493)
Balance at end of period	(56)	410	(56)	410
Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(5)	41	(5)	41
Other comprehensive income (loss) before classifications			0	0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			0	0
Other comprehensive income	0	0	0	0
Balance at end of period	$ (5)	$ 41	$ (5)	$ 41