Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Oil and gas properties:
Proved properties	$ 1,385,331	$ 1,337,215
Unproved properties	919,056	593,510
Support equipment and facilities	1,386,448	1,241,943
Total oil and gas properties	3,690,835	3,172,668
Less: accumulated depletion	(989,946)	(858,442)
Oil and gas properties, net	2,700,889	2,314,226
Other property	37,186	34,807
Less: accumulated depreciation	(29,183)	(26,194)
Other property, net	8,003	8,613
Property and equipment, net	2,708,892	2,322,839
Depletion expense	$ 131,500	$ 146,600	$ 188,300