Annual report pursuant to Section 13 and 15(d)

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

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Share-Based and Cash-Based Incentive Compensation - Summary of Share Activity Related to Restricted Stock Units (Details) - Restricted Stock Units (RSUs) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Nonvested, beginning of period 1,977,335 1,331,753 969,820
Granted 2,626,930 1,195,388 969,919
Vested (721,038) (354,692) (468,925)
Forfeited (409,148) (195,114) (139,061)
Nonvested, end of period 3,474,079 1,977,335 1,331,753
Weighted Average Grant Date Value, Beginning of period $ 15.29 $ 14.96 $ 22.70
Weighted Average Grant Date Fair Value, Granted 3.59 16.84 13.23
Weighted Average Grant Date Fair Value, Vested 13.23 18.59 26.93
Weighted Average Grant Date Fair Value, Forfeited 10.63 16.53 16.50
Weighted Average Grant Date Value, End of period $ 7.42 $ 15.29 $ 14.96