Repurchase Agreements Repurchase Agreements, Counterparty Information (Details) $ in Thousands	Mar. 31, 2017 USD ($) Agreements
Counterparty Information [Line Items]
Line of Credit Facility, Amount Outstanding	$ 345,672
Line of Credit Facility, Maximum Borrowing Capacity	$ 350,000
Line of Credit Facility, Interest Rate at Period End	1.85%
Number of Counterparties with Borrowings Outstanding | Agreements	18
Available Repurchase Agreement Counterparties | Agreements	31
Wells Fargo Bank, N. A. and affiliates
Counterparty Information [Line Items]
Borrowings outstanding with counterparty	$ 358,267
WAVG interest rate for amount outstanding with named counterparty	1.85%
Repurchase Agreement Counterparty, Amount at Risk	$ 64,695