Short and Long-Term Funding (Remaining Contractual Maturity of the Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 477,607	$ 383,568
Overnight and Continuous
Remaining Contractual Maturity of the Agreements
Repurchase agreements	477,607	383,568
Up to 30 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
30-90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Greater than 90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
GSE Securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	477,607	383,568
GSE Securities | Overnight and Continuous
Remaining Contractual Maturity of the Agreements
Repurchase agreements	477,607	383,568
GSE Securities | Up to 30 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
GSE Securities | 30-90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
GSE Securities | Greater than 90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 0	$ 0