Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income After-tax By Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 867,185	$ 603,804
Ending balance	846,436	797,835
Net Unrealized Gain (Loss) on Available-for-Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	14,977	(9,047)
Net change	10,561	11,722
Ending balance	25,538	2,675
Unamortized Gain (Loss) on Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	4,934	(235)
Net change	(156)	2
Ending balance	4,778	(233)
Net Unrealized Loss on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,162)	0
Net change	(5,057)	(952)
Ending balance	(7,219)	(952)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17,749	(9,282)
Net change	5,348	10,772
Ending balance	$ 23,097	$ 1,490