Supplemental Balance Sheet and Income Statement Information - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued liabilities
Accrued compensation	$ 92,152	$ 130,970
Deferred revenue	159,416	218,370
Other taxes payable	37,359	32,095
Workers' compensation liabilities	13,987	13,987
Interest payable	20,205	65,642
Litigation reserves	25,109	18,830
Current liability to discontinued operations	5,762	6,074
Dividends declared and payable	25,757	17,148
Other accrued liabilities	12,729	29,928
Accrued liabilities	$ 392,476	$ 533,044