Summary of Significant Accounting Policies - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 752,557	$ 708,146	$ 643,647
Beginning balance, as adjusted				$ 708,644
Other comprehensive income before reclassifications	(26,537)	(16,580)	24,077
Amounts reclassified from AOCI	(14,580)	(9,576)	(15,803)
Other comprehensive (loss)/income net of tax	(41,117)	(26,156)	8,274
Stranded tax effects reclassified from AOCI due to enactment of new tax legislation			9,053
Cumulative effect from change in hedge accounting				27
Ending balance	799,276	752,557	708,146
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	(25,360)	(1,676)	(14,387)
Beginning balance, as adjusted				(1,676)
Other comprehensive income before reclassifications	(14,976)	(19,151)	23,925
Amounts reclassified from AOCI	(3,061)	(4,533)	(10,917)
Other comprehensive (loss)/income net of tax	(18,037)	(23,684)	13,008
Stranded tax effects reclassified from AOCI due to enactment of new tax legislation			(297)
Cumulative effect from change in hedge accounting				0
Ending balance	(43,397)	(25,360)	(1,676)
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	43,443	48,236	45,752
Beginning balance, as adjusted				48,236
Other comprehensive income before reclassifications	0	0	0
Amounts reclassified from AOCI	(10,598)	(4,793)	(6,064)
Other comprehensive (loss)/income net of tax	(10,598)	(4,793)	(6,064)
Stranded tax effects reclassified from AOCI due to enactment of new tax legislation			8,548
Cumulative effect from change in hedge accounting				0
Ending balance	32,845	43,443	48,236
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,873	4,525	2,393
Beginning balance, as adjusted				4,552
Other comprehensive income before reclassifications	(11,561)	2,571	152
Amounts reclassified from AOCI	(921)	(250)	1,178
Other comprehensive (loss)/income net of tax	(12,482)	2,321	1,330
Stranded tax effects reclassified from AOCI due to enactment of new tax legislation			802
Cumulative effect from change in hedge accounting				27
Ending balance	(5,609)	6,873	4,525
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	24,956	51,085	33,758
Beginning balance, as adjusted				$ 51,112
Other comprehensive (loss)/income net of tax	(41,117)	(26,156)	8,274
Ending balance	$ (16,161)	$ 24,956	$ 51,085