Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Recorded Investment in Loans Modified in TDRs within Previous 12 months Subsequently Defaulted (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]
TDRs modified within the previous 12 months that defaulted in the period	$ 0	$ 24,304	$ 0	$ 27,336
Commercial loans | Software/internet
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs modified within the previous 12 months that defaulted in the period	0	19,625	0	22,657
Commercial loans | Hardware
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs modified within the previous 12 months that defaulted in the period	0	3,449	0	3,449
Commercial loans | Life science/healthcare
Financing Receivable, Troubled Debt Restructuring [Line Items]
TDRs modified within the previous 12 months that defaulted in the period	$ 0	$ 1,230	$ 0	$ 1,230