Comprehensive Income - Summary of Changes in Components of Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 623,739	$ 583,122
Cumulative adjustment for adoption of ASU 2016-01			$ 125
Adjusted equity balance			623,864		$ 583,122
Net current period other comprehensive (loss) income	4,149	(5,449)
Balance at end of period	681,343	588,648
Unrealized Losses on Available for Sale Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(8,782)	(3,232)
Cumulative adjustment for adoption of ASU 2016-01				$ 0		$ (2,043)
Adjusted equity balance				(8,782)		(5,275)
Net current period other comprehensive (loss) income	4,363	(5,732)
Balance at end of period	(4,419)	(11,007)
Unrealized Gains on Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	903	862
Cumulative adjustment for adoption of ASU 2016-01				0		0
Adjusted equity balance				903		862
Net current period other comprehensive (loss) income	(214)	283
Balance at end of period	689	1,145
Pension Items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	41	21
Cumulative adjustment for adoption of ASU 2016-01				0		0
Adjusted equity balance				41		21
Net current period other comprehensive (loss) income	0	0
Balance at end of period	41	21
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(7,838)	(2,349)
Cumulative adjustment for adoption of ASU 2016-01				0	(2,043)	(2,043)
Adjusted equity balance			$ (7,838)	$ (7,838)	$ (4,392)	$ (4,392)
Balance at end of period	$ (3,689)	$ (9,841)