Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax liabilities:
Property and equipment	$ (178,090)	$ (161,491)
Goodwill	(60,305)	(49,407)
Other intangibles	(21,034)	(26,676)
Customer holdbacks	(44,173)	(36,218)
Other book/tax accounting method differences	(7,247)	(17,967)
Total deferred income tax liabilities	(310,849)	(291,759)
Deferred income tax assets:
Accruals and reserves	28,594	21,419
Stock and incentive compensation	20,627	17,676
Net operating loss carryforwards	52,406	62,925
Tax credits	43,572	48,516
Deferred profit on investment in unconsolidated affiliates	16,021	2,813
Other	15,054	4,747
Subtotal	176,274	158,096
Valuation allowance	(67,601)	(19,328)	$ (15,000)
Total deferred income tax assets	108,673	138,768
Total net deferred income tax liabilities	$ (202,176)	$ (152,991)