Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 725,263	$ 623,739	$ 583,122
Other comprehensive income (loss) before classifications	10,021
Amounts reclassified from accumulated other comprehensive income	(872)
Other comprehensive income (loss)	9,149	10,086	(3,446)
Balance at end of period	763,784	725,263	623,739
Cumulated adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(3,395)	125
Balance at end of period		(3,395)	125
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	2,248	(7,838)	(2,349)
Other comprehensive income (loss)	9,149	10,086	(3,446)
Balance at end of period	11,397	2,248	(7,838)
Total | Cumulated adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(2,043)
Total | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(4,392)
Unrealized Gains (Losses)  on Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	1,936	(8,782)	(3,232)
Other comprehensive income (loss) before classifications	10,338
Amounts reclassified from accumulated other comprehensive income	(872)
Other comprehensive income (loss)	9,466	10,718	(3,507)
Balance at end of period	11,402	1,936	(8,782)
Unrealized Gains (Losses)  on Available- for-Sale Securities | Cumulated adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(2,043)
Unrealized Gains (Losses)  on Available- for-Sale Securities | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(5,275)
Unrealized Gains  (Losses) on  Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	317	903	862
Other comprehensive income (loss) before classifications	(292)
Amounts reclassified from accumulated other comprehensive income	0
Other comprehensive income (loss)	(292)	(586)	41
Balance at end of period	25	317	903
Unrealized Gains  (Losses) on  Derivatives | Cumulated adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			0
Unrealized Gains  (Losses) on  Derivatives | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			862
Pension Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(5)	41	21
Other comprehensive income (loss) before classifications	(25)
Amounts reclassified from accumulated other comprehensive income	0
Other comprehensive income (loss)	(25)	(46)	20
Balance at end of period	$ (30)	$ (5)	41
Pension Items | Cumulated adjustment for adoption of ASU
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			0
Pension Items | Adjusted balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			$ 21