Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of income tax expense from operations to the federal statutory rate
Income taxes computed at federal statutory rate	$ 73,200	$ 61,161	$ 43,280
State income taxes - net of federal benefit	7,347	7,196	5,114
Income taxes computed at the effective federal and state statutory rate for pass-through entities not subject to tax	(75,689)	(67,761)	(46,661)
Increase (decrease) of valuation allowance	1,049	735	(396)
Other		25	803
Income tax expense	$ 5,907	$ 1,356	$ 2,140