Securities Financing Activities - Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 2,818,461	$ 3,095,655
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	845,035	1,408,736
Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	1,578,613	806,526
30 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	394,813	880,393
Greater Than 90 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
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	2,741,913	3,013,351
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	845,035	1,408,736
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	1,578,613	806,526
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	318,265	798,089
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	0
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	76,548	82,304
Mortgage-backed securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
Mortgage-backed securities | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0	0
Mortgage-backed securities | 30 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	76,548	82,304
Mortgage-backed securities | Greater Than 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 0	$ 0