Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Income taxes (Summary of valuation allowance) (Details)

v3.8.0.1
Income taxes (Summary of valuation allowance) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Deferred Tax Assets, Valuation Allowance [Roll Forward]    
Valuation allowance at beginning of period $ 127,361 $ 72,000
(Decrease) increase of allowance to income tax provision (22,503) 55,361
Valuation allowance at end of period $ 104,858 $ 127,361