Carrying Value of Repurchase Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 489,620	$ 396,151
Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	489,620	394,513
Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	0	1,638
U.S. government and federal agency
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	4,402
U.S. government and federal agency | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	4,402
U.S. government and federal agency | 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	397,077	328,174
Residential mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	397,077	328,174
Residential mortgage-backed securities | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	0	0
Commercial mortgage-backed securities
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	88,141	67,977
Commercial mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	88,141	66,339
Commercial mortgage-backed securities | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 0	$ 1,638