Income Taxes - Components of Deferred Income Tax Amounts (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Income Tax Assets
Provision for bad debts	$ 11,092	$ 9,210
Deferred compensation and other benefit obligations	96,948	83,065
Workers’ compensation	8,206	9,138
Stock-based compensation	15,814	14,572
Credits and net operating loss carryforwards	35,499	39,309
Other	23,885	25,316
Total deferred income tax assets	191,444	180,610
Deferred Income Tax Liabilities
Amortization of intangible assets	(26,960)	(25,060)
Property and equipment basis differences	(11,890)	(12,384)
Other	(9,720)	(7,261)
Total deferred income tax liabilities	(48,570)	(44,705)
Valuation allowance	(26,329)	(29,561)
Total deferred income tax assets, net	$ 116,545	$ 106,344