Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 583,122	$ 550,044	$ 400,516
Other comprehensive loss	(3,446)	(2,522)	(557)
Adjustment for implementation of ASU 2018-02				$ 0
January 1, 2018, as adjusted				583,122
Balance at end of period	623,739	583,122	550,044
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	(3,232)	(117)	1,154
Other comprehensive income (loss) before classifications	(3,507)	(903)	(1,038)
Amounts reclassified from accumulated other comprehensive income	0	(1,640)	(233)
Other comprehensive loss	(3,507)	(2,543)	(1,271)
Adjustment for implementation of ASU 2018-02		(572)		(2,043)
January 1, 2018, as adjusted				(5,275)
Balance at end of period	(8,782)	(3,232)	(117)
Unrealized Gains (Losses) on Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	862	672	0
Other comprehensive income (loss) before classifications	41	37	672
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive loss	41	37	672
Adjustment for implementation of ASU 2018-02		153		0
January 1, 2018, as adjusted				862
Balance at end of period	903	862	672
Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	21	38	(4)
Other comprehensive income (loss) before classifications	20	(16)	42
Amounts reclassified from accumulated other comprehensive income	0	0	0
Other comprehensive loss	20	(16)	42
Adjustment for implementation of ASU 2018-02		(1)		0
January 1, 2018, as adjusted				21
Balance at end of period	41	21	38
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(2,349)	593	1,150
Other comprehensive income (loss) before classifications	(3,446)	(882)	(324)
Amounts reclassified from accumulated other comprehensive income	0	(1,640)	(233)
Other comprehensive loss	(3,446)	(2,522)	(557)
Adjustment for implementation of ASU 2018-02		(420)		(2,043)
January 1, 2018, as adjusted				$ (4,392)
Balance at end of period	$ (7,838)	$ (2,349)	$ 593