Additional Balance Sheet Detail and Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Other Accrued Liabilities	$ 11,883	$ 12,323
Accrued Income Taxes, Current	1,252	25,788
Accrual for Taxes Other than Income Taxes, Current	3,378	4,354
Interest Payable, Current	5,363	1,513
Accrued Salaries, Current	18,677	26,559
Business Combination, Contingent Consideration, Liability, Current	24,847	24,393
Accrued liabilities and other	$ 65,400	$ 94,930