Loans - Consumer Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,218,747	$ 14,155,267
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,012,516	9,747,429
Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,039,349	1,967,857
Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,478,673	1,510,540
Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	603,684	611,846
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,206,231	4,407,838
Consumer loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,643,306	5,694,740
Consumer loan portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,264,620	3,252,487
Consumer loan portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,572,240	1,613,008
Consumer loan portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	806,446	829,245
Consumer loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,121,706	4,090,243
Consumer loan portfolio | Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,039,349	1,967,857
Consumer loan portfolio | Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,478,673	1,510,540
Consumer loan portfolio | Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	603,684	611,846
Consumer loan portfolio | Originated | Performing
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,110,124	4,076,461
Consumer loan portfolio | Originated | Performing | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,031,728	1,959,222
Consumer loan portfolio | Originated | Performing | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,477,751	1,509,698
Consumer loan portfolio | Originated | Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	600,645	607,541
Consumer loan portfolio | Originated | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,582	13,782
Consumer loan portfolio | Originated | Nonperforming | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,621	8,635
Consumer loan portfolio | Originated | Nonperforming | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	922	842
Consumer loan portfolio | Originated | Nonperforming | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,039	4,305
Consumer loan portfolio | Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,521,600	1,604,497
Consumer loan portfolio | Acquired | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,225,271	1,284,630
Consumer loan portfolio | Acquired | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	93,567	102,468
Consumer loan portfolio | Acquired | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 202,762	$ 217,399