Other Noncurrent Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Liabilities, Other than Long-term Debt, Noncurrent [Abstract]
Tax amortization benefit contingency	$ 32,670	$ 31,562
Other	6,523	6,943
Total other noncurrent liabilities	$ 39,193	$ 38,505