Fair Value Measurements - Hierarchy (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value Measurements at Reporting Date
Derivative assets	$ 6,644	$ 1,311
Derivative liabilities	(3,851)	(8,168)
Quoted Prices in Active Markets for Identical Assets/(Liabilities) (Level 1)
Fair Value Measurements at Reporting Date
Derivative assets	2,018	18
Derivative liabilities	(3,851)	(8,168)
Significant Other Observable Inputs (Level 2)
Fair Value Measurements at Reporting Date
Derivative assets	$ 4,626	$ 1,293