Consolidated Statements of Stockholders' Equity - 9 months ended Sep. 30, 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)	$ 75,686	$ 73,615	$ 2,071
Balance at at Sep. 30, 2018	$ 470,699
Balance at (in shares) at Sep. 30, 2018	59,080,387