Securities - Schedule of Unrealized Loss and Fair Value on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value
Less than 12 months	$ 332,677	$ 664,476
12 months or longer	440,333	198,397
Total	773,010	862,873
Unrealized Losses
Less than 12 months	(2,290)	(13,451)
12 months or longer	(10,541)	(4,992)
Total	(12,831)	(18,443)
Collateralized Loan Obligations [Member]
Fair Value
Less than 12 months	14,933	8,152
12 months or longer	0	51,694
Total	14,933	59,846
Unrealized Losses
Less than 12 months	(68)	(41)
12 months or longer	0	(938)
Total	(68)	(979)
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	1,107
12 months or longer	0
Total	1,107
Unrealized Losses
Less than 12 months	(5)
12 months or longer	0
Total	(5)
Mortgage-backed securities of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	123,195	327,759
12 months or longer	213,590	5,387
Total	336,785	333,146
Unrealized Losses
Less than 12 months	(515)	(5,991)
12 months or longer	(4,183)	(75)
Total	(4,698)	(6,066)
Collateralized Mortgage Obligations Of US Government Sponsored Entities [Member]
Fair Value
Less than 12 months	176,452	234,175
12 months or longer	199,086	58,912
Total	375,538	293,087
Unrealized Losses
Less than 12 months	(1,507)	(5,599)
12 months or longer	(5,955)	(2,096)
Total	(7,462)	(7,695)
Commercial mortgage backed securities of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	5,076	7,934
12 months or longer	1,049	0
Total	6,125	7,934
Unrealized Losses
Less than 12 months	(25)	(102)
12 months or longer	(9)	0
Total	(34)	(102)
Private mortgage backed securities [Member]
Fair Value
Less than 12 months	0	0
12 months or longer	0	36,848
Total	0	36,848
Unrealized Losses
Less than 12 months	0	0
12 months or longer	0	(900)
Total	0	(900)
Private collateralized mortgage obligations [Member]
Fair Value
Less than 12 months	0	1,460
12 months or longer	20,744	38,417
Total	20,744	39,877
Unrealized Losses
Less than 12 months	0	0
12 months or longer	(338)	(816)
Total	(338)	(816)
Obligations of state and political subdivisions [Member]
Fair Value
Less than 12 months	5,414	39,321
12 months or longer	5,864	0
Total	11,278	39,321
Unrealized Losses
Less than 12 months	(14)	(895)
12 months or longer	(56)	0
Total	(70)	(895)
Corporate and other debt securities [member]
Fair Value
Less than 12 months	6,500	33,008
12 months or longer	0	0
Total	6,500	33,008
Unrealized Losses
Less than 12 months	(156)	(517)
12 months or longer	0	0
Total	$ (156)	(517)
Private commercial mortgage backed securities [Member]
Fair Value
Less than 12 months		12,667
12 months or longer		7,139
Total		19,806
Unrealized Losses
Less than 12 months		(306)
12 months or longer		(167)
Total		$ (473)