Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plan (Details)

v3.8.0.1
Equity Incentive Plan (Details)
 12 Months Ended
Nov. 01, 2017
Dec. 31, 2017
$ / shares
shares
Dec. 31, 2016
$ / shares
shares
Dec. 31, 2015
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of restricted common shares reserved for issuance under equity incentive plan (in shares) | shares   6,500,000    
Reverse stock split, conversion ratio 0.50      
Number of restricted common shares granted during period under equity incentive plan (in shares) | shares   671,845 1,009,630  
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) | $ / shares   $ 17.60 $ 15.11  
Award vesting period of restricted common shares granted during period under equity incentive plan   3 years    
Director [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of restricted common shares granted during period under equity incentive plan (in shares) | shares   34,559 40,869 30,976
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) | $ / shares   $ 19.82 $ 16.86 $ 20.36
Key Employees [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of restricted common shares granted during period under equity incentive plan (in shares) | shares   637,286 968,761 557,787
Weighted average grant date fair value of restricted common shares granted during period under equity incentive plan (in usd per share) | $ / shares   $ 17.48 $ 15.04 $ 20.97
Common stock share price (in usd per share) | $ / shares   $ 16.26