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Status Summary of Non-Vested Shares (Detail) - Performance Shares - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Beginning balance 103,907 24,637  
Number of Shares, Granted 10,696 79,270 24,637
Number of Shares, Forfeited (10,200)    
Number of Shares, Ending Balance 104,403 103,907 24,637
Weighted Average Grant-Date Fair Value, Beginning balance $ 17.77 $ 28.28  
Weighted Average Grant-Date Fair Value, Granted 11.38 14.51  
Weighted Average Grant-Date Fair Value, Forfeited 18.43    
Weighted Average Grant-Date Fair Value, Ending balance $ 17.05 $ 17.77 $ 28.28