Fair Value Measurements - Summary of Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial assets
Current derivative assets	$ 3,626	$ 3,569
Noncurrent derivative assets	287
Fair Value on a Recurring Basis [Member]
Financial assets
Current derivative assets	3,626	3,569
Noncurrent derivative assets	287
Net Recognized Assets	3,913	3,569
Fair Value on a Recurring Basis [Member] | Level 2 [Member]
Financial assets
Current derivative assets	3,626	3,569
Noncurrent derivative assets	287
Net Recognized Assets	$ 3,913	$ 3,569