Fair Value Measurement (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (82,155)	$ (37,253)
Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(3,438)	2,196
Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(30,339)	2,263
Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(48,378)	(41,712)
Commodity contract derivatives
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(7,064)	4,459
Commodity contract derivatives | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(3,438)	2,196
Commodity contract derivatives | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(3,626)	2,263
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	(26,713)
Convertible debt conversion liability | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0
Convertible debt conversion liability | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(26,713)
Convertible debt conversion liability | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0
Contingent considerations for acquisitions
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(48,378)	(41,712)
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	$ (48,378)	$ (41,712)