Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent			$ (882)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 623,739	$ 583,122	550,044
Other comprehensive loss	10,086	(3,446)	(2,522)
Adjustment related to implementation of ASU 2018-02			0
January 1, as adjusted				$ 623,864	$ 583,122
Balance at end of period	725,263	623,739	583,122
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			(1,640)
Other comprehensive income (loss), net of tax	10,086	(3,446)	(2,522)
Unrealized Gains (Losses) on Available- for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent			(903)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(8,782)	(3,232)	(117)
Adjustment related to implementation of ASU 2018-02		(2,043)	(572)
January 1, as adjusted					(5,275)
Balance at end of period	1,936	(8,782)	(3,232)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			(1,640)
Other comprehensive income (loss), net of tax	10,718	(3,507)	(2,543)
Unrealized Gains (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent			37
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	903	862	672
Adjustment related to implementation of ASU 2018-02		0	153
January 1, as adjusted					862
Balance at end of period	317	903	862
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			0
Other comprehensive income (loss), net of tax	(586)	41	37
Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
OCI, before Reclassifications, Net of Tax, Attributable to Parent			(16)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	41	21	38
Adjustment related to implementation of ASU 2018-02		0	(1)
January 1, as adjusted					21
Balance at end of period	(5)	41	21
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent			0
Other comprehensive income (loss), net of tax	(46)	20	(16)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(7,838)	(2,349)	593
Adjustment related to implementation of ASU 2018-02		(2,043)	(420)
January 1, as adjusted				$ (7,838)	$ (4,392)
Balance at end of period	2,248	(7,838)	(2,349)
Other comprehensive income (loss), net of tax	$ 10,086	$ (3,446)	$ (2,522)