Portfolio Loans - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
financing receivable, paycheck protection program		$ 709,900
financing receivable, paycheck protection program, net of deferred fees		698,600
financing recievable, paycheck protection program, unearned fees		11,300
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available		2,500,000
net premium, acquired loans		16,100
net discount, acquired loans		36,000
Allowance for credit losses on loans			$ 43,288
financing receivable, amount eligible for deferred payment		687,800
Financing Receivable, Amount Eligible for Deferral of Both Principal and Interest		340,000
financing receivable, amount eligible for deferral of principal only		347,800
Financing Receivable, Amount Still in Deferral Status		63,000
Loans and Leases Receivable, Deferred Income		4,100
Allowance for Credit Losses, Qualitative Adjustment		24,000
Cumulative Effect, Period of Adoption, Adjustment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses on loans		28,387
enterprise value lending portfolio niche segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Credit Losses, Qualitative Adjustment		11,100
Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses on loans	$ 69,995	136,671	42,567	$ 42,295	$ 38,166
CECL adoption	28,387
Financing Receivable, Credit Loss, Expense (Reversal)	1,680	63,400	$ 6,700
financing receivable, allowance for credit loss, threshold of loans written off	$ 100
Non-Covered Loans | Cumulative Effect, Period of Adoption, Adjustment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses on loans		5,900
Non-Covered Loans | enterprise value lending portfolio niche segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses on loans		19,000
Unadvanced Commitment on Impaired Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated losses attributable to unadvanced commitments on impaired loans		$ 5,700