Income Taxes - Components of Deferred Income Tax Amounts (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Income Tax Assets
Provision for bad debts	$ 10,510	$ 11,092
Deferred compensation and other benefit obligations	112,811	96,948
Workers’ compensation	5,634	8,206
Stock-based compensation	16,772	15,814
Credits and net operating loss carryforwards	30,534	35,499
Other	18,116	23,885
Total deferred income tax assets	194,377	191,444
Deferred Income Tax Liabilities
Amortization of intangible assets	(28,681)	(26,960)
Property and equipment basis differences	(16,640)	(11,890)
Other	(11,658)	(9,720)
Total deferred income tax liabilities	(56,979)	(48,570)
Valuation allowance	(18,907)	(26,329)
Total deferred income tax assets, net	$ 118,491	$ 116,545