Supplemental Balance Sheet and Income Statement Information - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued liabilities
Accrued compensation	$ 74,104	$ 92,358
Deferred revenue	95,100	116,700
Deferred revenue and proceeds on insurance and asset sales	125,777	149,266
Other taxes payable	15,460	33,199
Workers' compensation liabilities	15,214	16,316
Interest payable	18,982	59,718
Litigation reserves	20,494	24,926
Current liability to discontinued operations	999	2,445
Dividends declared and payable	3,514	25,330
Other accrued liabilities	23,515	14,354
Accrued liabilities	$ 298,059	$ 417,912