Loans - Recorded Investment Based on Payment Activity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 6,242,907	$ 6,220,351
Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,660,983	3,682,984
Non-PCI Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	381,217	371,340
Non-PCI Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,347,405	1,319,206
Non-PCI Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	853,302	846,821
Non-PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,228,808	6,204,779
Non-PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,649,062	3,670,067
Non-PCI Loans | Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	379,411	369,184
Non-PCI Loans | Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,347,257	1,319,126
Non-PCI Loans | Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	853,078	846,402
Non-PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	14,099	15,572
Non-PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	11,921	12,917
Non-PCI Loans | Non-Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,806	2,156
Non-PCI Loans | Non-Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	148	80
Non-PCI Loans | Non-Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	224	419
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,004,340	4,190,086
PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	410,254	428,416
PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	145,406	160,263
PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	718,185	740,657
PCI Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,476,037	2,494,966
PCI Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	254,458	365,784
PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,948,158	4,133,961
PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	405,111	421,609
PCI Loans | Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	143,577	158,502
PCI Loans | Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	690,301	710,045
PCI Loans | Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,455,693	2,478,990
PCI Loans | Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	253,476	364,815
PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	56,182	56,125
PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	5,143	6,807
PCI Loans | Non-Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,829	1,761
PCI Loans | Non-Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	27,884	30,612
PCI Loans | Non-Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	20,344	15,976
PCI Loans | Non-Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 982	$ 969