Additional Balance Sheet Detail and Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Other Accrued Liabilities	$ 13,688	$ 12,323
Accrued Income Taxes, Current	16,474	25,788
Accrual for Taxes Other than Income Taxes, Current	3,639	4,354
Interest Payable, Current	1,589	1,513
Accrued Salaries, Current	22,229	26,559
Business Combination, Contingent Consideration, Liability, Current	25,000	24,393
Accrued liabilities and other	$ 82,619	$ 94,930