Additional Balance Sheet Detail and Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Other Accrued Liabilities	$ 12,290	$ 12,323
Accrued Income Taxes, Current	2,649	25,788
Accrual for Taxes Other than Income Taxes, Current	3,741	4,354
Interest Payable, Current	1,545	1,513
Accrued Salaries, Current	16,745	26,559
Business Combination, Contingent Consideration, Liability, Current	24,694	24,393
Accrued liabilities and other	$ 61,664	$ 94,930