Loans - Consumer Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,796,252	$ 14,155,267
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,145,442	9,747,429
Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,285,611	1,967,857
Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,483,540	1,510,540
Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	613,931	611,846
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,650,810	4,407,838
Consumer loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,742,562	5,694,740
Consumer loan portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,391,987	3,252,487
Consumer loan portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,560,265	1,613,008
Consumer loan portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	790,310	829,245
Consumer loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,383,082	4,090,243
Consumer loan portfolio | Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,285,611	1,967,857
Consumer loan portfolio | Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,483,540	1,510,540
Consumer loan portfolio | Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	613,931	611,846
Consumer loan portfolio | Originated | Performing
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,368,852	4,076,461
Consumer loan portfolio | Originated | Performing | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,276,000	1,959,222
Consumer loan portfolio | Originated | Performing | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,482,190	1,509,698
Consumer loan portfolio | Originated | Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	610,662	607,541
Consumer loan portfolio | Originated | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,230	13,782
Consumer loan portfolio | Originated | Nonperforming | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,611	8,635
Consumer loan portfolio | Originated | Nonperforming | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,350	842
Consumer loan portfolio | Originated | Nonperforming | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,269	4,305
Consumer loan portfolio | Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,359,480	1,604,497
Consumer loan portfolio | Acquired | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,106,376	1,284,630
Consumer loan portfolio | Acquired | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	76,725	102,468
Consumer loan portfolio | Acquired | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 176,379	$ 217,399