Accumulated Other Comprehensive Income (Loss) - Reclassifications out of AOCI - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	$ (9,075)	$ (3,624)
Other noninterest income	2,575	1,674
Provision for income taxes	(11,285)	(7,103)
Net income	42,326	18,264
Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Net income	188	185
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	47	110
Provision for income taxes	(10)	(42)
Net income	37	68
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	188
Provision for income taxes	(43)	(71)
Net income	$ 151	$ 117