Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets
Gross amounts of derivatives recognized at fair value	$ 2,999	$ 14,901
Cash collateral	3,817	2,870
Total gross amount recognized	6,816	17,771
Gross amounts offset	(680)	(4,833)
Net amount reported in the condensed consolidated balance sheet	6,136	12,938
Liabilities
Gross amounts of derivatives recognized at fair value	(680)	205
Cash collateral	0	4,628
Total gross amount recognized	(680)	4,833
Gross amounts offset	680	(4,833)
Net amount reported in the condensed consolidated balance sheet	$ 0	$ 0