Comprehensive Income - Summary of Changes in Components of Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 745,489	$ 698,463	$ 725,263	$ 623,739
Other comprehensive income (loss) before classifications			8,884	11,048
Amounts reclassified from accumulated other comprehensive income			(254)	0
Other comprehensive income, net of tax	(539)	1,402	8,630	11,048
Balance at end of period	753,572	713,204	753,572	713,204
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	11,417	1,808	2,248	(7,838)
Other comprehensive income, net of tax	(539)	1,402	8,630	11,048
Balance at end of period	10,878	3,210	10,878	3,210
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	11,478	1,357	1,936	(8,782)
Other comprehensive income (loss) before classifications			9,220	11,619
Amounts reclassified from accumulated other comprehensive income			(254)	0
Other comprehensive income, net of tax	(576)	1,480	8,966	11,619
Balance at end of period	10,902	2,837	10,902	2,837
Unrealized Gains (Losses) on Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(56)	410	317	903
Other comprehensive income (loss) before classifications			(336)	(571)
Amounts reclassified from accumulated other comprehensive income			0	0
Other comprehensive income, net of tax	37	(78)	(336)	(571)
Balance at end of period	(19)	332	(19)	332
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
Amounts reclassified from accumulated other comprehensive income			0	0
Other comprehensive income, net of tax	0	0	0	0
Balance at end of period	$ (5)	$ 41	$ (5)	$ 41

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