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Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Cash and Investments in Marketable Securities [Line Items]          
Maximum maturity term for debt securities investment     Two years or less    
Weighted average maturity term for debt securities investment     One year or less    
Available-for-sale securities, sold $ 0.0 $ 0.0 $ 5,200,000 $ 0.0  
Restricted cash 25,000,000   25,000,000   $ 25,000,000
Level 1 to level 2 transfers 0 0 0 0  
Level 2 to level 1 transfers 0 $ 0 0 $ 0  
Senior secured notes, carrying amount 125,000,000   125,000,000   $ 125,000,000
12% Senior Secured Notes Due July 2017 [Member]          
Cash and Investments in Marketable Securities [Line Items]          
Restricted cash $ 25,000,000   $ 25,000,000    
Senior secured notes, interest rate 12.00%   12.00%    
Senior secured notes, maturity date     Jul. 15, 2017    
12% Senior Secured Notes Due July 2017 [Member] | Level 3 [Member]          
Cash and Investments in Marketable Securities [Line Items]          
Senior secured notes, interest rate 12.00%   12.00%    
Senior secured notes, maturity date     Jul. 15, 2017    
Senior secured notes, carrying amount $ 125,000,000   $ 125,000,000