Securities - Schedule of Unrealized Loss and Fair Value on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value
Less than 12 months	$ 598,333	$ 326,177
12 months or longer	507,551	440,333
Total	1,105,884	766,510
Unrealized Losses
Less than 12 months	(12,937)	(2,134)
12 months or longer	(21,718)	(10,540)
Total	(34,655)	(12,674)
Collateralized loan obligations
Fair Value
Less than 12 months	138,769	14,933
12 months or longer	0	0
Total	138,769	14,933
Unrealized Losses
Less than 12 months	(502)	(68)
12 months or longer	0	0
Total	(502)	(68)
Mortgage-backed securities and collateralized mortgage obligations of U.S. Government Sponsored Entities
Fair Value
Less than 12 months	420,280	304,723
12 months or longer	468,753	413,725
Total	889,033	718,448
Unrealized Losses
Less than 12 months	(12,087)	(2,047)
12 months or longer	(20,976)	(10,146)
Total	(33,063)	(12,193)
Private collateralized mortgage obligations
Fair Value
Less than 12 months	25,971	0
12 months or longer	18,468	20,744
Total	44,439	20,744
Unrealized Losses
Less than 12 months	(210)	0
12 months or longer	(291)	(338)
Total	(501)	(338)
Obligations of state and political subdivisions
Fair Value
Less than 12 months	9,896	5,414
12 months or longer	20,330	5,864
Total	30,226	11,278
Unrealized Losses
Less than 12 months	(94)	(14)
12 months or longer	(451)	(56)
Total	(545)	(70)
U.S. Treasury securities and obligations of U.S. Government Entities
Fair Value
Less than 12 months	3,417	1,107
12 months or longer	0	0
Total	3,417	1,107
Unrealized Losses
Less than 12 months	(44)	(5)
12 months or longer	0	0
Total	$ (44)	$ (5)