Supplementary Balance Sheet Information - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Supplementary Balance Sheet Information
Prepaid expenses	$ 63,847	$ 65,159
Income taxes receivable	42,934	41,400
R and D state tax credit	22,642	22,642
Supplies inventory	17,465	17,072
Other	77,796	70,292
Total	$ 224,684	$ 216,565