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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 773,742	$ 763,298	$ 752,557	$ 766,212	$ 745,266	$ 708,146	$ 752,557	$ 708,146
Cumulative effect from change in hedge accounting										$ 27
Adjusted Beginning Balance											$ 708,644
Other comprehensive (loss)/income before reclassifications	(23,986)			(7,285)			(53,987)	19,943
Amounts reclassified from AOCI	(6,195)			(2,124)			(13,993)	(7,054)
Other comprehensive (loss)/income net of tax	(30,181)	(34,097)	(3,702)	(9,409)	1,299	20,999	(67,980)	12,889
Ending balance	750,259	773,742	763,298	777,591	766,212	745,266	750,259	777,591
Total [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(12,843)	21,254	24,956	73,410	72,111	51,085	24,956	51,085
Adjusted Beginning Balance									$ 24,956	51,112	$ 51,112
Other comprehensive (loss)/income net of tax	(30,181)	(34,097)	(3,702)	(9,409)	1,299	20,999
Ending balance	(43,024)	(12,843)	21,254	64,001	73,410	72,111	(43,024)	64,001
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] | Available-for-sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(45,384)		(25,360)	15,882		(1,676)	(25,360)	(1,676)
Adjusted Beginning Balance									(25,360)	(1,676)
Other comprehensive (loss)/income before reclassifications	(18,915)			(9,947)			(37,308)	10,450
Amounts reclassified from AOCI	(776)			(755)			(2,407)	(3,594)
Other comprehensive (loss)/income net of tax	(19,691)			(10,702)			(39,715)	6,856
Ending balance	(65,075)	(45,384)		5,180	15,882		(65,075)	5,180
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] | Held-to-maturity Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	38,021		43,443	45,979		48,236	43,443	48,236
Adjusted Beginning Balance									43,443	48,236
Other comprehensive (loss)/income before reclassifications	0			0			0	0
Amounts reclassified from AOCI	(5,169)			(1,220)			(10,591)	(3,477)
Other comprehensive (loss)/income net of tax	(5,169)			(1,220)			(10,591)	(3,477)
Ending balance	32,852	38,021		44,759	45,979		32,852	44,759
Cash Flow Hedge [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,480)		$ 6,873	11,549		$ 4,525	6,873	4,525
Cumulative effect from change in hedge accounting										27
Adjusted Beginning Balance									$ 6,873	$ 4,552
Other comprehensive (loss)/income before reclassifications	(5,071)			2,662			(16,679)	9,493
Amounts reclassified from AOCI	(250)			(149)			(995)	17
Other comprehensive (loss)/income net of tax	(5,321)			2,513			(17,674)	9,510
Ending balance	$ (10,801)	$ (5,480)		$ 14,062	$ 11,549		$ (10,801)	$ 14,062