Derivative Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Gross amounts of derivatives recognized at fair value	$ 4,664	$ 812
Cash collateral	3,172	8,799
Total gross amount recognized	7,836	9,611
Gross amounts offset	(3,162)	(8,001)
Net amount reported in the condensed consolidated balance sheets	4,674	1,610
Liabilities
Gross amounts of derivatives recognized at fair value	3,162	8,001
Cash collateral	0	0
Total gross amount recognized	3,162	8,001
Gross amounts offset	(3,162)	(8,001)
Net amount reported in the condensed consolidated balance sheets	$ 0	$ 0