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

Earnings per share (Narrative) (Details)

v3.8.0.1
Earnings per share (Narrative) (Details) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Earnings Per Share [Abstract]      
Unvested restricted stock (in shares) (3,007,752) (3,426,810) (3,030,724)
Number of shares excluded from diluted shares outstanding (in shares) 509,677 152,314 36,666