Allowance for Credit Losses - Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 138,762	$ 116,446	$ 120,856	$ 114,419
Loans charged-off	(1,983)	(1,729)	(5,904)	(9,397)
Charged-off loans recovered	1,752	2,948	6,285	6,531
Net recoveries (charge-offs)	(231)	1,219	381	(2,866)
Provision for loan losses	6,432	1,301	23,726	7,413
Ending balance	144,963	118,966	144,963	118,966
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	74,257	51,617	57,232	50,820
Loans charged-off	(833)	(265)	(1,606)	(4,889)
Charged-off loans recovered	1,131	2,320	4,057	3,480
Net recoveries (charge-offs)	298	2,055	2,451	(1,409)
Provision for loan losses	9,442	1,017	24,314	5,278
Ending balance	83,997	54,689	83,997	54,689
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	53,812	55,455	54,954	55,851
Loans charged-off	0	0	(348)	(553)
Charged-off loans recovered	12	42	396	824
Net recoveries (charge-offs)	12	42	48	271
Provision for loan losses	(3,694)	(198)	(4,872)	(823)
Ending balance	50,130	55,299	50,130	55,299
Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,624	4,186	3,605	3,702
Loans charged-off	0	(129)	(167)	(488)
Charged-off loans recovered	9	220	269	903
Net recoveries (charge-offs)	9	91	102	415
Provision for loan losses	286	(385)	1,212	(225)
Ending balance	4,919	3,892	4,919	3,892
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	6,069	5,188	5,065	4,046
Loans charged-off	(1,150)	(1,335)	(3,783)	(3,467)
Charged-off loans recovered	600	366	1,563	1,324
Net recoveries (charge-offs)	(550)	(969)	(2,220)	(2,143)
Provision for loan losses	398	867	3,072	3,183
Ending balance	$ 5,917	$ 5,086	$ 5,917	$ 5,086