Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Summary of Recorded Investment in Loans Modified in TDRs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	$ 68,157	$ 22,968	$ 68,773	$ 26,017
Loans classified as TDRs, charge-offs	3,400	8,500	5,600
Commercial loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	66,292	22,968	66,908	25,692
Commercial loans | Software/internet
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	55,065	14,783	55,681	14,783
Commercial loans | Hardware
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	0	1,954	0	3,448
Commercial loans | Life science/healthcare
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	11,227	6,231	11,227	7,461
Consumer loans | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	1,865	0	1,865	325
Payment deferrals granted
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period	$ 66,300	$ 23,000	66,900	$ 26,000
Partial principal forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable modifications recorded investment modified during period			$ 1,900