Consolidated Statements of Stockholders' Equity - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at at Dec. 31, 2017	$ 395,279
Balance at (in shares) at Dec. 31, 2017	59,057,195
Stock-based compensation plans
Total comprehensive income (loss)	$ 16,591	$ 15,878	$ 713
Balance at at Mar. 31, 2018	$ 408,498
Balance at (in shares) at Mar. 31, 2018	59,080,512