Summary of Significant Accounting Policies - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 799,276	$ 752,557
Other comprehensive (loss)/income before reclassifications	(100,353)	(777)
Amounts reclassified from AOCI	(4,923)	(2,925)
Other comprehensive loss net of tax	(105,276)	(3,702)
Ending balance	693,617	763,298
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	(43,397)	(25,360)
Other comprehensive (loss)/income before reclassifications	(77,685)	3,318
Amounts reclassified from AOCI	(776)	(758)
Other comprehensive loss net of tax	(78,461)	2,560
Ending balance	(121,858)	(22,800)
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	32,845	43,443
Other comprehensive (loss)/income before reclassifications	0	0
Amounts reclassified from AOCI	(4,494)	(1,787)
Other comprehensive loss net of tax	(4,494)	(1,787)
Ending balance	28,351	41,656
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,609)	6,873
Other comprehensive (loss)/income before reclassifications	(22,668)	(4,095)
Amounts reclassified from AOCI	347	(380)
Other comprehensive loss net of tax	(22,321)	(4,475)
Ending balance	(27,930)	2,398
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(16,161)	24,956
Other comprehensive loss net of tax	(105,276)	(3,702)
Ending balance	$ (121,437)	$ 21,254