Securities - Schedule of Unrealized Loss and Fair Value on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value
Less than 12 months	$ 540,638	$ 326,177
12 months or longer	438,084	440,333
Total	978,722	766,510
Unrealized Losses
Less than 12 months	(10,355)	(2,134)
12 months or longer	(16,959)	(10,540)
Total	(27,314)	(12,674)
Collateralized Loan Obligations [Member]
Fair Value
Less than 12 months	12,747	14,933
12 months or longer	0	0
Total	12,747	14,933
Unrealized Losses
Less than 12 months	(3)	(68)
12 months or longer	0	0
Total	(3)	(68)
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	895	1,107
12 months or longer	0	0
Total	895	1,107
Unrealized Losses
Less than 12 months	(14)	(5)
12 months or longer	0	0
Total	(14)	(5)
Mortgage-backed securities of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	257,394	123,195
12 months or longer	214,042	213,590
Total	471,436	336,785
Unrealized Losses
Less than 12 months	(4,629)	(515)
12 months or longer	(7,756)	(4,183)
Total	(12,385)	(4,698)
Collateralized Mortgage Obligations Of US Government Sponsored Entities [Member]
Fair Value
Less than 12 months	242,193	176,452
12 months or longer	188,936	199,086
Total	431,129	375,538
Unrealized Losses
Less than 12 months	(5,403)	(1,507)
12 months or longer	(8,565)	(5,954)
Total	(13,968)	(7,461)
Commercial mortgage backed securities of U.S. Government Sponsored Entities [Member]
Fair Value
Less than 12 months	7,925	5,076
12 months or longer	3,032	1,049
Total	10,957	6,125
Unrealized Losses
Less than 12 months	(78)	(25)
12 months or longer	(72)	(9)
Total	(150)	(34)
Private collateralized mortgage obligations [Member]
Fair Value
Less than 12 months	762	0
12 months or longer	19,586	20,744
Total	20,348	20,744
Unrealized Losses
Less than 12 months	(1)	0
12 months or longer	(312)	(338)
Total	(313)	(338)
Obligations of state and political subdivisions [Member]
Fair Value
Less than 12 months	18,722	5,414
12 months or longer	12,488	5,864
Total	31,210	11,278
Unrealized Losses
Less than 12 months	(227)	(14)
12 months or longer	(254)	(56)
Total	$ (481)	$ (70)