Accumulated Other Comprehensive Income (Loss) - Reclassifications out of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	$ (12,170)	$ (3,748)	$ (21,245)	$ (7,372)
Other noninterest income	2,503	1,491	5,078	3,165
Provision for income taxes	(11,644)	(15,930)	(22,929)	(23,033)
Net income	40,459	31,823	82,785	50,087
Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Net income	682	61	870	269
Gains on sales of available for sale securities | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Securities (gains) losses, net	641	(110)	641	(110)
Provision for income taxes	(141)	43	(141)	42
Net income	500	(67)	500	(68)
Gains on sales of available for sale securities | Amount Reclassified from Accumulated Other Comprehensive Loss | Interest rate contracts
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	39	19	87	168
Provision for income taxes	(8)	(7)	(19)	(64)
Net income	31	12	68	104
Amortization of defined benefit pension | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Salaries and employee benefits	194	187	387	376
Provision for income taxes	(43)	(71)	(85)	(143)
Net income	$ 151	$ 116	$ 302	$ 233