Income Taxes - Tax Expense Components and Reconciliation to Federal Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense:
Federal	$ 45,809	$ 54,726	$ 63,626
State and local	8,331	13,329	10,868
Total current income tax expense	54,140	68,055	74,494
Deferred income tax expense (benefit)	(72,324)	(12,591)	(2,058)
Total income tax expense (benefit)	$ (18,184)	$ 55,464	$ 72,436
Differences between the expected income tax expense and income taxes computed at the federal statutory rate
Federal income tax at statutory rate	35.00%	35.00%	35.00%
State and local income taxes, less federal income tax benefit	3.70%	3.60%	4.00%
Permanent differences	1.70%	1.40%	1.40%
Tax benefit from the sale of businesses	0.00%	(6.70%)	0.00%
Valuation allowance	(7.30%)	0.20%	(0.90%)
Uncertain tax positions	(0.60%)	(1.30%)	(2.30%)
Non-controlling interest	0.50%	(0.50%)	(2.00%)
Stock-based compensation	(1.30%)	(0.70%)	0.00%
Deferred income taxes - state income tax rate adjustment	(2.80%)	0.00%	0.00%
Deferred income taxes - tax legislation rate adjustment	(37.50%)	0.00%	0.00%
Other	(0.40%)	(0.30%)	(0.40%)
Total effective income tax rate	(9.00%)	30.70%	34.80%