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Summary of Significant Accounting Policies - Basic and Diluted Shares Outstanding (Detail) - $ / shares
shares in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]      
Weighted average common shares outstanding - basic 21,127 20,772 20,364
Effect of dilutive options (in shares) 69 49 37
Weighted average common shares outstanding - diluted 21,196 20,821 20,401
Average share price (in usd per share) $ 53.38 $ 49.09 $ 45.44
Options      
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]      
Antidilutive options (in shares) 111 107 113