Annual report pursuant to Section 13 and 15(d)

Share-Based Awards and Cash-Based Awards - Summary of Share Activity Related to Restricted Stock Units (Details)

v3.8.0.1
Share-Based Awards and Cash-Based Awards - Summary of Share Activity Related to Restricted Stock Units (Details) - Restricted Stock Units (RSUs) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Nonvested, beginning of period 6,107,248 3,474,079 1,977,335
Granted 2,128,879 4,213,964 2,626,930
Vested (2,108,553) (968,652) (721,038)
Forfeited (362,323) (612,143) (409,148)
Nonvested, end of period 5,765,251 6,107,248 3,474,079
Weighted Average Grant Date Value, Beginning of period $ 2.73 $ 7.42 $ 15.29
Weighted Average Grant Date Fair Value, Granted 2.76 2.21 3.59
Weighted Average Grant Date Fair Value, Vested 3.45 16.69 13.23
Weighted Average Grant Date Fair Value, Forfeited 2.87 3.64 10.63
Weighted Average Grant Date Value, End of period $ 2.48 $ 2.73 $ 7.42