Summary of Significant Accounting Policies - Basic and Diluted Shares Outstanding (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted average common shares outstanding - basic (in shares)	21,505	21,127	20,772
Effect of dilutive options (in shares)	110	69	49
Weighted average common shares outstanding - diluted (in shares)	21,615	21,196	20,821
Average share price (in usd per share)	$ 58.96	$ 53.38	$ 49.09
Options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive options (in shares)	129	111	107