Borrowings Summary of Repurchase Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 396,151	$ 362,573
Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	394,513	362,573
Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	1,638	0
Residential mortgage backed securities
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	328,174	360,751
Residential mortgage backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	328,174	360,751
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	67,977	1,822
Commercial mortgage backed securities | Overnight and Continuous
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	66,339	1,822
Commercial mortgage backed securities | Up to 30 Days
Securities Sold Under Agreements to Repurchase
Repurchase Agreements	$ 1,638	$ 0