Loans - Consumer Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 13,833,368	$ 12,990,779
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,156,096	7,458,401
Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,881,285	1,475,342
Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,502,814	1,282,588
Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	622,565	595,422
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,677,272	5,532,378
Consumer loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,696,012	5,396,567
Consumer loan portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,221,307	3,086,474
Consumer loan portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,615,983	1,433,884
Consumer loan portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	858,722	876,209
Consumer loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,006,664	3,353,352
Consumer loan portfolio | Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,881,285	1,475,342
Consumer loan portfolio | Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,502,814	1,282,588
Consumer loan portfolio | Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	622,565	595,422
Consumer loan portfolio | Originated | Performing
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,993,235	3,342,153
Consumer loan portfolio | Originated | Performing | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,872,639	1,468,373
Consumer loan portfolio | Originated | Performing | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,501,939	1,281,709
Consumer loan portfolio | Originated | Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	618,657	592,071
Consumer loan portfolio | Originated | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,429	11,199
Consumer loan portfolio | Originated | Nonperforming | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,646	6,969
Consumer loan portfolio | Originated | Nonperforming | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	875	879
Consumer loan portfolio | Originated | Nonperforming | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,908	3,351
Consumer loan portfolio | Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,689,348	2,043,215
Consumer loan portfolio | Acquired | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,340,022	1,611,132
Consumer loan portfolio | Acquired | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	113,169	151,296
Consumer loan portfolio | Acquired | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 236,157	$ 280,787