Carrying Value of Repurchase Agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 441,041	$ 397,107
Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	438,217
Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	2,824
U.S. government sponsored enterprises
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	12,603
U.S. government sponsored enterprises | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	12,603
U.S. government sponsored enterprises | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	0
Residential mortgage-backed securities
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	428,438	397,107
Residential mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	425,614	391,997
Residential mortgage-backed securities | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 2,824	$ 5,110