Fair Value Measurement (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (67,887)	$ (75,907)
Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	1,531	(1,297)
Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(26,241)	(28,042)
Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(43,177)	(46,568)
Commodity contract derivatives
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	2,562	(2,239)
Commodity contract derivatives | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	1,531	(1,297)
Commodity contract derivatives | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	1,031	(942)
Commodity contract derivatives | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Convertible debt conversion liability
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(27,272)	(27,100)
Convertible debt conversion liability | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Convertible debt conversion liability | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(27,272)	(27,100)
Convertible debt conversion liability | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(43,177)	(46,568)
Contingent considerations for acquisitions | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (43,177)	$ (46,568)