Fair Value Measurements - Schedule of fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
FAIR VALUE MEASUREMENTS
Noncontrolling interests subject to put provisions	$ 126,483	$ 129,099
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)
FAIR VALUE MEASUREMENTS
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)	3,000
Recurring basis
FAIR VALUE MEASUREMENTS
Total Assets	143	1,231
Total Liabilities	4,508	3,700
Noncontrolling interests subject to put provisions	126,483	129,099
Recurring basis | Interest rate derivative agreements (included in Prepaid expenses and other current assets)
FAIR VALUE MEASUREMENTS
Total Assets	143	836
Recurring basis | Interest rate derivative agreements (included in Other long-term assets)
FAIR VALUE MEASUREMENTS
Total Assets		395
Recurring basis | Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)
FAIR VALUE MEASUREMENTS
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)	3,000	3,700
Recurring basis | Interest rate derivative agreements (included in Accrued expense and other current liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	783
Recurring basis | Interest rate derivative agreements (included in Other long-term liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	725
Recurring basis | Level 1
FAIR VALUE MEASUREMENTS
Total Assets	0	0
Total Liabilities	0	0
Noncontrolling interests subject to put provisions	0	0
Recurring basis | Level 1 | Interest rate derivative agreements (included in Prepaid expenses and other current assets)
FAIR VALUE MEASUREMENTS
Total Assets	0	0
Recurring basis | Level 1 | Interest rate derivative agreements (included in Other long-term assets)
FAIR VALUE MEASUREMENTS
Total Assets		0
Recurring basis | Level 1 | Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)
FAIR VALUE MEASUREMENTS
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)	0	0
Recurring basis | Level 1 | Interest rate derivative agreements (included in Accrued expense and other current liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	0
Recurring basis | Level 1 | Interest rate derivative agreements (included in Other long-term liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	0
Recurring basis | Level 2
FAIR VALUE MEASUREMENTS
Total Assets	143	1,231
Total Liabilities	1,508	0
Noncontrolling interests subject to put provisions	0	0
Recurring basis | Level 2 | Interest rate derivative agreements (included in Prepaid expenses and other current assets)
FAIR VALUE MEASUREMENTS
Total Assets	143	836
Recurring basis | Level 2 | Interest rate derivative agreements (included in Other long-term assets)
FAIR VALUE MEASUREMENTS
Total Assets		395
Recurring basis | Level 2 | Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)
FAIR VALUE MEASUREMENTS
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)	0	0
Recurring basis | Level 2 | Interest rate derivative agreements (included in Accrued expense and other current liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	783
Recurring basis | Level 2 | Interest rate derivative agreements (included in Other long-term liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	725
Recurring basis | Level 3
FAIR VALUE MEASUREMENTS
Total Assets	0	0
Total Liabilities	3,000	3,700
Noncontrolling interests subject to put provisions	126,483	129,099
Recurring basis | Level 3 | Interest rate derivative agreements (included in Prepaid expenses and other current assets)
FAIR VALUE MEASUREMENTS
Total Assets	0	0
Recurring basis | Level 3 | Interest rate derivative agreements (included in Other long-term assets)
FAIR VALUE MEASUREMENTS
Total Assets		0
Recurring basis | Level 3 | Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)
FAIR VALUE MEASUREMENTS
Tax Receivable Agreement Liability (included in Income tax receivable agreement payable)	3,000	$ 3,700
Recurring basis | Level 3 | Interest rate derivative agreements (included in Accrued expense and other current liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	0
Recurring basis | Level 3 | Interest rate derivative agreements (included in Other long-term liabilities)
FAIR VALUE MEASUREMENTS
Interest rate swap agreements liability	$ 0