Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plan Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity (Details)

v3.8.0.1
Equity Incentive Plan Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]    
Number of nonvested restricted common shares outstanding at beginning of period (in shares) 1,319,712 1,145,305
Weighted average grant date fair value of nonvested restricted common shares outstanding at beginning of period (in usd per share) $ 17.10 $ 20.73
Number of restricted common shares granted during period under equity incentive plan (in 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) $ 17.60 $ 15.11
Number of restricted common shares vested during period (in shares) (684,727) (684,614)
Weighted average grant date fair value of restricted common shares vested during period (in usd per share) $ (17.47) $ (20.26)
Number of restricted common shares forfeited during period (in shares) (22,820) (150,609)
Weighted average grant date fair value of restricted common shares forfeited during period (in usd per share) $ (17.90) $ (17.01)
Number of nonvested restricted common shares outstanding at end of period (in shares) 1,284,010 1,319,712
Weighted average grant date fair value of nonvested restricted common shares outstanding at end of period (in usd per share) $ 17.15 $ 17.10