Additional Balance Sheet Detail and Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Other Accrued Liabilities	$ 6,179	$ 13,688
Accrued Income Taxes, Current	8,825	16,474
Accrual for Taxes Other than Income Taxes, Current	2,974	3,639
Interest Payable, Current	5,173	1,589
Operating Lease, Liability, Current	13,340	0
Accrued Salaries, Current	16,190	22,229
Business Combination, Contingent Consideration, Liability, Current	49,455	25,000
Accrued liabilities and other	$ 102,136	$ 82,619