Income Taxes - Deferred Tax Assets and Liabilities Recognized in Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Noncurrent deferred tax asset — Other noncurrent assets	$ 2,958	$ 2,265
Noncurrent deferred tax liabilities — Deferred income taxes	(137,638)	(166,427)
Total deferred tax (liabilities), net of valuation allowances	$ (134,680)	$ (164,162)