v2.4.0.8
Long-Term Debt - Additional Information1 (Detail) (USD $)
 6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Debt Instrument [Line Items]    
Long-term debt $ 730,214,000 $ 735,701,000
Interest at a weighted-average fixed rate 1.20% 1.20%
Amount reduced under revolving credit facilities in remaining 2013 12,600,000  
Amount reduced under revolving credit facilities in 2014 25,200,000  
Amount reduced under revolving credit facilities in 2015 58,500,000  
Amount reduced under revolving credit facilities in 2016 108,100,000  
Amount reduced under revolving credit facilities in 2017 415,300,000  
Amount reduced under revolving credit facilities thereafter 110,500,000  
Secured Debt [Member]
    
Debt Instrument [Line Items]    
Number of debt instruments 3  
Long-term debt 172,182,000 180,229,000
Minimum hull coverage ratio 120.00%  
Number of first priority mortgages granted on vessels as debt collateral 6  
Maintain the greater of free cash liquidity for revolving credit facility $ 100,000,000  
Minimum percentage to maintaining revolving credit facility 7.50%  
Secured Debt [Member] | Minimum [Member]
    
Debt Instrument [Line Items]    
Term loan fixed interest rate 4.06%  
Percentage of margin 0.30% 0.30%
Actual hull coverage ratio 127.00%  
Secured Debt [Member] | Maximum [Member]
    
Debt Instrument [Line Items]    
Term loan fixed interest rate 4.90%  
Percentage of margin 1.00% 1.00%
Actual hull coverage ratio 311.00%