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Quarterly Results for 2016 and 2015 - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]                      
Percentage of decrease in net income 53.20%                    
Decrease in net income during period $ 15,500                    
Net income $ 13,655 $ 26,882 $ 33,647 $ 25,226 $ 29,152 $ 30,298 $ 24,704 $ 22,330 $ 99,410 $ 106,484 $ 72,988