Supplemental Balance Sheet, Income Statement and Cash Flow Information - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued liabilities
Accrued compensation	$ 105,571	$ 130,970
Deferred revenue	202,712	218,370
Other taxes payable	18,042	32,095
Workers' compensation liabilities	13,987	13,987
Interest payable	27,587	65,642
Litigation reserves	21,394	18,830
Current liability to discontinued operations	5,978	6,074
Dividends declared and payable	19,052	17,148
Other accrued liabilities	17,971	29,928
Accrued liabilities	$ 432,294	$ 533,044