Loans - Consumer Loans by Risk Rating Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 15,861,903	$ 15,269,779
Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	12,871,110	11,844,756
Originated | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,722,019	2,407,305
Originated | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,497,467	1,451,352
Originated | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	604,835	612,129
Acquired
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,990,793	3,425,023
Consumer loan portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	5,966,048	5,757,912
Consumer loan portfolio | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,666,613	3,458,666
Consumer loan portfolio | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,552,835	1,521,074
Consumer loan portfolio | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	746,600	778,172
Consumer loan portfolio | Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,824,321	4,470,786
Consumer loan portfolio | Originated | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,722,019	2,407,305
Consumer loan portfolio | Originated | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,497,467	1,451,352
Consumer loan portfolio | Originated | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	604,835	612,129
Consumer loan portfolio | Originated | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,811,787	4,457,918
Consumer loan portfolio | Originated | Performing | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,714,383	2,399,317
Consumer loan portfolio | Originated | Performing | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,496,056	1,450,076
Consumer loan portfolio | Originated | Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	601,348	608,525
Consumer loan portfolio | Originated | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	12,534	12,868
Consumer loan portfolio | Originated | Nonperforming | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	7,636	7,988
Consumer loan portfolio | Originated | Nonperforming | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,411	1,276
Consumer loan portfolio | Originated | Nonperforming | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,487	3,604
Consumer loan portfolio | Acquired
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,141,727	1,287,126
Consumer loan portfolio | Acquired | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	944,594	1,051,361
Consumer loan portfolio | Acquired | Consumer installment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	55,368	69,722
Consumer loan portfolio | Acquired | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 141,765	$ 166,043