Repurchase Agreement Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 157,569	$ 164,966
Pledged Assets Separately Reported, Securities Pledged for Repurchase Agreements, at Fair Value	206,000	272,000
Available unpledged securities	877,000	933,000
Maturity Overnight [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	157,569	164,966
Maturity up to 30 days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	0	0
Maturity 30 to 90 Days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	0	0
Maturity over 90 days [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 0	$ 0