Securities - Schedule of Unrealized Loss and Fair Value on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value
Less Than 12 Months	$ 339,727	$ 478,423
12 Months or Longer	512,271	646,354
Total	851,998	1,124,777
Unrealized Losses
Less Than 12 Months	(2,551)	(7,140)
12 Months or Longer	(10,431)	(19,538)
Total	(12,982)	(26,678)
Collateralized loan obligations
Fair Value
Less Than 12 Months	238,777	238,894
12 Months or Longer	0	0
Total	238,777	238,894
Unrealized Losses
Less Than 12 Months	(1,809)	(4,319)
12 Months or Longer	0	0
Total	(1,809)	(4,319)
Mortgage-backed securities and collateralized mortgage obligations of U.S. Government Sponsored Entities
Fair Value
Less Than 12 Months	80,889	200,184
12 Months or Longer	496,722	623,420
Total	577,611	823,604
Unrealized Losses
Less Than 12 Months	(512)	(2,235)
12 Months or Longer	(10,217)	(19,136)
Total	(10,729)	(21,371)
Private mortgage-backed securities and collateralized mortgage obligations
Fair Value
Less Than 12 Months	20,061	20,071
12 Months or Longer	2,038	12,739
Total	22,099	32,810
Unrealized Losses
Less Than 12 Months	(230)	(344)
12 Months or Longer	(9)	(187)
Total	(239)	(531)
Obligations of state and political subdivisions
Fair Value
Less Than 12 Months	0	19,175
12 Months or Longer	12,966	9,553
Total	12,966	28,728
Unrealized Losses
Less Than 12 Months	0	(241)
12 Months or Longer	(201)	(210)
Total	(201)	(451)
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities
Fair Value
Less Than 12 Months	0	99
12 Months or Longer	545	642
Total	545	741
Unrealized Losses
Less Than 12 Months	0	(1)
12 Months or Longer	(4)	(5)
Total	$ (4)	$ (6)