Summary of Significant Accounting Policies - Shares Used in Computation of Basic and Diluted Per Share Information (Detail) - shares	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
Weighted Average Shares Outstanding:
Weighted average number of shares outstanding for basic per share calculation	17,597,190	17,588,163	17,566,097	17,485,766	17,447,691	17,436,731	17,410,971	17,322,791	17,559,477	17,405,379	17,229,026
Effect of dilutive potential shares:
Options									863	3,663	4,284
Nonvested Stock Awards									122,480	138,489	82,023
Weighted Average Number of Shares Outstanding, Diluted (shares)	17,764,066	17,719,473	17,685,147	17,633,549	17,647,483	17,610,953	17,529,100	17,489,483	17,682,820	17,547,531	17,315,333
Antidilutive shares									219,855	200,525	173,360