Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of income tax expense from operations to the federal statutory rate
Income taxes computed at federal statutory rate	$ 136,485	$ 73,200	$ 61,161
State income taxes - net of federal benefit	13,723	7,347	7,196
Federal alternative minimum tax and state and local taxes on pass-through entities	1,072	1,013	1,179
Income taxes computed at the effective federal and state statutory rate for pass-through entities not subject to tax	(86,200)	(76,702)	(68,940)
Increase in valuation allowance	11,194	1,049	735
Impact of 2017 Tax Act	79,987
Other	721		25
Income tax expense	156,982	$ 5,907	$ 1,356
Tax Receivable Agreement liability adjustment	$ (38,399)