Share-Based Compensation - Profits Interests (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vested in period, fair value	$ 371	$ 345
Profit Interests
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Outstanding at beginning of period (in shares)	14,061,530	12,616,890
Granted (in shares)	2,920,000	295,000
Forfeited (in shares)	(800,000)	(400,000)
Redeemed (in shares)	0	0
Effect of Reorganization Transactions and IPO (in shares)	(16,181,530)
Outstanding at beginning of period (in shares)	0	12,511,890
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding at beginning of period (in dollars per share)	$ 8.23
Granted (in dollars per share)	14.31
Forfeited (in dollars per share)	9.32
Effect of Reorganization Transactions and IPO (in dollars per share)	9.27
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Grants in period, weighted average grant date fair value (in dollars per share)	$ 4.47	$ 2.89