Supplementary Balance Sheet Information - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Supplementary Balance Sheet Information
Prepaid expenses	$ 43,458	$ 65,159
Income taxes receivable	38,615	41,400
R and D state tax credit	26,346	22,642
Supplies inventory	19,401	17,072
Other	69,190	70,292
Total	$ 197,010	$ 216,565