Equity Incentive Plans - Equity Appreciation Rights (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Aggregate Intrinsic Value
Share-based compensation	$ 15,285	$ 14,494	$ 2,033
Equity Appreciation Rights
Equity Incentive Plans
Accrued compensation and benefits		$ 151,500
Number of Awards
Outstanding at beginning of the period	7,614,000	9,180,000
Settled (in shares)	(7,614,000)	(1,566,000)
Outstanding at end of the period		7,614,000	9,180,000
Weighted Average Exercise Price
Outstanding at beginning of the period	$ 19.90	$ 11.40
Settled	$ (19.90)	11.12
Outstanding at end of the period		$ 19.90	$ 11.40
Additional Information
Weighted-Average Remaining Contractual Term			1 year
Aggregate Intrinsic Value
Outstanding at beginning of the period	$ 151,511	$ 171,712
Outstanding at end of the period		151,511	$ 171,712
Share-based compensation		$ 6,000	$ 45,800