Equity-Based Compensation - 2005 Common Membership Unit Plan (Details) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended		12 Months Ended			36 Months Ended
	Nov. 30, 2015	Feb. 28, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Notes receivable issued to members, including accrued interest					$ 18,301
2005 Common Membership Unit Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of units (in units)	1,758					21,440
Options settled (in shares)		4,286		160	3,536
Exercise price of options	$ 3,900
Related payroll taxes	1,500
Total settlement value	$ 5,400
2005 Common Membership Unit Plan | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of units (in units)		2,433
Notes receivable issued to members, including accrued interest		$ 18,300
Options settled (in shares)		4,293
2005 Common Membership Unit Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of award			10 years