Carrying Value of Repurchase Agreements (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 494,651,000	$ 396,151,000
Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	494,651,000	394,513,000
Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	0	1,638,000
Residential mortgage-backed securities
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	295,255,000	328,174,000
Residential mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	295,255,000	328,174,000
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	199,396,000	67,977,000
Commercial mortgage-backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	199,396,000	66,339,000
Commercial mortgage-backed securities | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 0	$ 1,638,000