Summary of Significant Accounting Policies - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 824,116	$ 693,617	$ 799,276	$ 773,742	$ 763,298	$ 752,557	$ 799,276	$ 752,557
Other comprehensive income/(loss) before reclassifications	39,003			(23,986)			(29,894)	(53,987)
Amounts reclassified from AOCI	(1,343)			(6,195)			(7,782)	(13,993)
Other comprehensive income/(loss) net of tax	37,660	29,940	(105,276)	(30,181)	(34,097)	(3,702)	(37,676)	(67,980)
Ending balance	930,345	824,116	693,617	750,259	773,742	763,298	930,345	750,259
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest | Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(88,261)		(43,397)	(45,384)		(25,360)	(43,397)	(25,360)
Other comprehensive income/(loss) before reclassifications	38,099			(18,915)			(5,210)	(37,308)
Amounts reclassified from AOCI	(783)			(776)			(2,338)	(2,407)
Other comprehensive income/(loss) net of tax	37,316			(19,691)			(7,548)	(39,715)
Ending balance	(50,945)	(88,261)		(65,075)	(45,384)		(50,945)	(65,075)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest | Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	26,379		32,845	38,021		43,443	32,845	43,443
Other comprehensive income/(loss) before reclassifications	0			0			0	0
Amounts reclassified from AOCI	(1,993)			(5,169)			(8,459)	(10,591)
Other comprehensive income/(loss) net of tax	(1,993)			(5,169)			(8,459)	(10,591)
Ending balance	24,386	26,379		32,852	38,021		24,386	32,852
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(29,615)		(5,609)	(5,480)		6,873	(5,609)	6,873
Other comprehensive income/(loss) before reclassifications	904			(5,071)			(24,684)	(16,679)
Amounts reclassified from AOCI	1,433			(250)			3,015	(995)
Other comprehensive income/(loss) net of tax	2,337			(5,321)			(21,669)	(17,674)
Ending balance	(27,278)	(29,615)		(10,801)	(5,480)		(27,278)	(10,801)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(91,497)	(121,437)	(16,161)	(12,843)	21,254	24,956	(16,161)	24,956
Other comprehensive income/(loss) net of tax	37,660	29,940	(105,276)	(30,181)	(34,097)	(3,702)
Ending balance	$ (53,837)	$ (91,497)	$ (121,437)	$ (43,024)	$ (12,843)	$ 21,254	$ (53,837)	$ (43,024)