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Fair Value Measurements - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Jul. 18, 2013
Sep. 30, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Carrying amount of senior notes   $ 224,125,000 $ 224,035,000
Other Asset Class [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Assets fair value on recurring basis   $ 0  
6.625% senior notes due 2021 [Member] | Senior notes [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Interest rate 6.625% 6.625% 6.625%
Due date Jul. 15, 2021 Jul. 15, 2021 Jul. 15, 2021
Carrying amount of senior notes   $ 224,125,000 $ 224,035,000
Estimated fair value of senior notes   $ 174,490,000