Equity-Based Compensation - Stock Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Stock options
Outstanding at the beginning of the period (in shares)	660,512
Options forfeited (in shares)	(80,895)
Outstanding at the end of the period (in shares)	579,617	660,512
Vested or expected to vest (in shares)	579,617
Exercisable (in shares)	462,217
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 50.48
Options forfeited (in dollars per share)	50.00
Outstanding at the end of the period (in dollars per share)	50.55	$ 50.48
Vested or expected to vest (in dollars per share)	50.55
Exercisable (in dollars per share)	$ 50.69
Weighted average remaining contractual life
Outstanding	5 years 9 months 22 days	7 years 22 days
Vested or expected to vest	5 years 9 months 22 days
Exercisable	5 years 8 months 9 days
Weighted-average assumptions used to calculate fair value of stock options granted
Dividend yield (as a percent)	0.00%
Additional disclosures
Unrecognized stock-based compensation expense	$ 0.5
Weighted average period for recognizing unrecognized stock-based compensation expense	3 months 18 days
Maximum
Stock-based compensation
Contractual life	10 years