Loans Receivable - Summary of Originated and Acquired Loans (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	$ 8,836,874,000	$ 8,808,674,000
Allowance for credit losses	(92,897,000)	(57,941,000)	$ (55,721,000)	$ (55,214,000)
Total loans receivable, net	8,743,977,000	8,750,733,000
Loans held-for-sale	6,426,000	7,709,000
Unearned income, unamortized premiums and discounts and deferred fees and costs	44,700,000	40,200,000
Personal Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	5,382,126,000	5,336,177,000
Allowance for credit losses	(37,619,000)	(18,356,000)
Personal Banking | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	2,834,733,000	2,868,127,000
Allowance for credit losses	(10,673,000)	(2,574,000)
Loans held-for-sale	6,400,000	7,700,000	0
Personal Banking | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	1,360,654,000	1,343,427,000
Allowance for credit losses	(9,786,000)	(3,189,000)
Personal Banking | Vehicle loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	936,827,000
Loans and Leases Receivable, Gross	936,827,000	861,192,000
Allowance for credit losses	(11,994,000)	(7,292,000)
Personal Banking | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	249,912,000	263,431,000
Allowance for credit losses	(5,166,000)	(5,301,000)
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	3,454,748,000	3,472,497,000
Allowance for credit losses	(55,278,000)	(39,585,000)
Commercial Banking | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	2,262,998,000	2,228,109,000
Allowance for credit losses	(29,380,000)	(15,843,000)
Commercial Banking | Commercial real estate loans - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	487,760,000	526,281,000
Allowance for credit losses	(8,374,000)	(5,745,000)
Commercial Banking | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	703,990,000	718,107,000
Allowance for credit losses	(17,524,000)	(17,997,000)
Originated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	8,080,528,000	7,987,057,000
Allowance for credit losses	(82,431,000)	(51,439,000)	(51,711,000)	(51,751,000)
Total loans receivable, net	7,998,097,000	7,935,618,000
Originated | Personal Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	5,060,438,000	4,973,850,000
Allowance for credit losses			(18,602,000)	(18,318,000)
Originated | Personal Banking | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	2,758,695,000	2,785,189,000
Allowance for credit losses			(4,005,000)	(4,054,000)
Originated | Personal Banking | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	1,129,370,000	1,100,023,000
Allowance for credit losses			(3,062,000)	(3,184,000)
Originated | Personal Banking | Vehicle loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	929,204,000
Loans and Leases Receivable, Gross		850,804,000
Originated | Personal Banking | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	243,169,000	237,834,000
Allowance for credit losses			(11,535,000)	(11,080,000)
Originated | Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	3,020,090,000	3,013,207,000
Allowance for credit losses			(33,109,000)	(33,433,000)
Originated | Commercial Banking | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	1,953,458,000	1,915,949,000
Allowance for credit losses			(25,470,000)	(26,379,000)
Originated | Commercial Banking | Commercial real estate loans - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	416,283,000	433,099,000
Originated | Commercial Banking | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	650,349,000	664,159,000
Allowance for credit losses			(7,639,000)	(7,054,000)
Acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	756,346,000	821,617,000
Allowance for credit losses	(10,466,000)	(6,502,000)	(4,010,000)	(3,463,000)
Total loans receivable, net	745,880,000	815,115,000
Acquired | Personal Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	321,688,000	362,327,000
Allowance for credit losses			(945,000)	(850,000)
Acquired | Personal Banking | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	76,038,000	82,938,000
Allowance for credit losses			(92,000)	(83,000)
Acquired | Personal Banking | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	231,284,000	243,404,000
Allowance for credit losses			(399,000)	(348,000)
Acquired | Personal Banking | Vehicle loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	7,623,000	10,388,000
Acquired | Personal Banking | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	6,743,000	25,597,000
Allowance for credit losses			(454,000)	(419,000)
Acquired | Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	434,658,000	459,290,000
Acquired | Commercial Banking | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses			(2,467,000)	(1,996,000)
Acquired | Commercial Banking | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses			(598,000)	(617,000)
Acquired | Commercial Banking | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses			$ (3,065,000)	$ (2,613,000)
Acquired | Commercial Banking | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	309,540,000	312,160,000
Acquired | Commercial Banking | Commercial real estate loans - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	71,477,000	93,182,000
Acquired | Commercial Banking | Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans receivable, gross	$ 53,641,000	$ 53,948,000