Fair Value Measurements - Fair Value Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other disclosures
Impairment of long-lived asset	$ 0	$ 4,772	$ 0
Series I Warrant Liabilities
Reconciliation of the beginning and ending balances of items measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance	2,046	7,164
Gain included in earnings	(1,414)	(5,748)
Ending Balance	632	2,046	$ 7,164
Series I Warrant Liabilities | NG Advantage
Reconciliation of the beginning and ending balances of items measured at fair value using significant unobservable inputs (Level 3)
Warrants acquired from NG Advantage acquisition	$ 0	$ 630