Supplemental Balance Sheet and Income Statement Information - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accrued liabilities
Accrued compensation	$ 115,874	$ 130,970
Deferred revenue	190,296	218,370
Other taxes payable	27,148	32,095
Workers' compensation liabilities	13,987	13,987
Interest payable	76,719	65,642
Litigation reserves	25,265	18,830
Current liability to discontinued operations	5,457	6,074
Dividends declared and payable	25,141	17,148
Other accrued liabilities	12,900	29,928
Accrued liabilities	$ 492,787	$ 533,044