Borrowings (Other Significant Details) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
DisclosureOfRepurchaseAgreementsAbstract
Average Daily Aggregate Balance Outstanding	$ 393,133	$ 663,845
Maximum Outstanding Balance At Any Month End	$ 606,210	$ 902,500
Repurchase agreement weighted average interest rate during the year	1.80%	2.83%
Weighted average interest rate at year end	1.63%	2.47%