Description of Business - Proforma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenues	$ 1,359,901	$ 1,238,730
Net income	$ (69,574)	$ 29,924
Diluted earnings (loss) per share (in dollars per share)	$ (2.10)	$ 0.85