Quarterly report pursuant to Section 13 or 15(d)

Equity-Based Compensation - Summary of Equity Grants (Detail)

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Equity-Based Compensation - Summary of Equity Grants (Detail) - $ / shares
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Performance Units    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Beginning Balance, Units 96,971 238,371
Vested, Units (90,585) (140,549)
Forfeited, Units   (851)
Ending Balance, Units 6,386 96,971
Beginning Balance, Range of Fair Value per unit $ 3.75 $ 3.75
Ending Balance, Range of Fair Value per unit $ 3.75 $ 3.75
Deferred Equity Units    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Beginning Balance, Units 52,188 175,298
Vested, Units (47,277) (123,110)
Ending Balance, Units 4,911 52,188
Deferred Equity Units | Minimum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Beginning Balance, Range of Fair Value per unit $ 12.00 $ 12.00
Vested, Range of Fair Value per unit (12.00) 12.00
Ending Balance, Range of Fair Value per unit 12.00 12.00
Deferred Equity Units | Maximum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Beginning Balance, Range of Fair Value per unit 15.65 17.05
Vested, Range of Fair Value per unit (13.97) (16.81)
Ending Balance, Range of Fair Value per unit $ 14.06 $ 17.21