Loans - Consumer Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 15,324,048	$ 15,269,779
Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,142,274	11,844,756
Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,542,943	2,407,305
Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,440,193	1,451,352
Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	603,144	612,129
Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,181,774	3,425,023
Consumer loan portfolio
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,812,217	5,757,912
Consumer loan portfolio | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,549,617	3,458,666
Consumer loan portfolio | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,504,441	1,521,074
Consumer loan portfolio | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	758,159	778,172
Consumer loan portfolio | Originated
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,586,280	4,470,786
Consumer loan portfolio | Originated | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,542,943	2,407,305
Consumer loan portfolio | Originated | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,440,193	1,451,352
Consumer loan portfolio | Originated | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	603,144	612,129
Consumer loan portfolio | Originated | Performing
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,574,151	4,457,918
Consumer loan portfolio | Originated | Performing | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,535,278	2,399,317
Consumer loan portfolio | Originated | Performing | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,439,002	1,450,076
Consumer loan portfolio | Originated | Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	599,871	608,525
Consumer loan portfolio | Originated | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,129	12,868
Consumer loan portfolio | Originated | Nonperforming | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,665	7,988
Consumer loan portfolio | Originated | Nonperforming | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,191	1,276
Consumer loan portfolio | Originated | Nonperforming | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,273	3,604
Consumer loan portfolio | Acquired
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,225,937	1,287,126
Consumer loan portfolio | Acquired | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,006,674	1,051,361
Consumer loan portfolio | Acquired | Consumer installment
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,248	69,722
Consumer loan portfolio | Acquired | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 155,015	$ 166,043