Securities - Schedule of Unrealized Loss and Fair Value on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value
Less than 12 months	$ 478,423	$ 326,177
12 months or longer	646,354	440,333
Total	1,124,777	766,510
Unrealized Losses
Less than 12 months	(7,140)	(2,134)
12 months or longer	(19,538)	(10,540)
Total	(26,678)	(12,674)
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities
Fair Value
Less than 12 months	99	1,107
12 months or longer	642	0
Total	741	1,107
Unrealized Losses
Less than 12 months	(1)	(5)
12 months or longer	(5)	0
Total	(6)	(5)
Mortgage-backed securities and collateralized mortgage obligations of US Government Sponsored Entities
Fair Value
Less than 12 months	200,184	304,723
12 months or longer	623,420	413,725
Total	823,604	718,448
Unrealized Losses
Less than 12 months	(2,235)	(2,047)
12 months or longer	(19,136)	(10,146)
Total	(21,371)	(12,193)
Private collateralized mortgage obligations
Fair Value
Less than 12 months	20,071	0
12 months or longer	12,739	20,744
Total	32,810	20,744
Unrealized Losses
Less than 12 months	(344)	0
12 months or longer	(187)	(338)
Total	(531)	(338)
Collateralized loan obligations
Fair Value
Less than 12 months	238,894	14,933
12 months or longer	0	0
Total	238,894	14,933
Unrealized Losses
Less than 12 months	(4,319)	(68)
12 months or longer	0	0
Total	(4,319)	(68)
Obligations of state and political subdivisions
Fair Value
Less than 12 months	19,175	5,414
12 months or longer	9,553	5,864
Total	28,728	11,278
Unrealized Losses
Less than 12 months	(241)	(14)
12 months or longer	(210)	(56)
Total	$ (451)	$ (70)