Investment Securities - Gross Unrealized Losses of Aggregated by Investment Category and Length of Time that Individual Securities have been in Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	$ 11,130	$ 17,505
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(427)	(178)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	176,077	183,064
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(5,865)	(3,976)
Temporarily Impaired Securities, Available for sale securities, Fair Value	187,207	200,569
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(6,292)	(4,154)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	183,492	145,374
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(3,530)	(1,091)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	22,222	6,462
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(599)	(98)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	205,714	151,836
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(4,129)	(1,189)
Temporarily Impaired Securities, Fair Value, Less than 12 months	194,622	162,879
Temporarily Impaired Securities, Unrealized Losses, Less than 12 months	(3,957)	(1,269)
Temporarily Impaired Securities, Fair Value, 12 months or longer	198,299	189,526
Temporarily Impaired Securities, Unrealized Losses, 12 months or longer	(6,464)	(4,074)
Temporarily Impaired Securities, Fair Value	392,921	352,405
Temporarily Impaired Securities, Unrealized Losses	(10,421)	(5,343)
U.S. GSE Obligations
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months		4,979
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months		(21)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	88,358	83,812
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(1,655)	(1,209)
Temporarily Impaired Securities, Available for sale securities, Fair Value	88,358	88,791
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(1,655)	(1,230)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	27,283	27,407
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(289)	(166)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	4,924
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(76)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	32,207	27,407
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(365)	(166)
Mortgage Backed Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	11,130	12,526
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(427)	(157)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	83,774	94,663
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(4,131)	(2,649)
Temporarily Impaired Securities, Available for sale securities, Fair Value	94,904	107,189
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(4,558)	(2,806)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	134,947	115,926
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(2,839)	(906)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	11,065	3
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(212)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	146,012	115,929
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(3,051)	(906)
Corporate Debt Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	3,945	3,990
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(79)	(45)
Temporarily Impaired Securities, Available for sale securities, Fair Value	3,945	3,990
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(79)	(45)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	6,830
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(138)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	6,830
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(138)
Mutual Funds
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer		599
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer		(73)
Temporarily Impaired Securities, Available for sale securities, Fair Value		599
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses		(73)
Municipal Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	14,432	2,041
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(264)	(19)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	6,233	6,459
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(311)	(98)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	20,665	8,500
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	$ (575)	$ (117)