Securities Financing Activities - Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 233,517	$ 85,632
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	172,071	4,906
Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
30 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	61,446	75,745
Greater Than 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	4,981
U.S. Treasury and other U.S. government agencies
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	172,071	22,787
U.S. Treasury and other U.S. government agencies | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	172,071	4,906
U.S. Treasury and other U.S. government agencies | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
U.S. Treasury and other U.S. government agencies | 30 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	12,900
U.S. Treasury and other U.S. government agencies | Greater Than 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	4,981
Agency mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	61,446	62,845
Agency mortgage-backed securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
Agency mortgage-backed securities | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
Agency mortgage-backed securities | 30 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	61,446	62,845
Agency mortgage-backed securities | Greater Than 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 0	$ 0