Stock-Based Incentive Plan - Compensation Expense Related to Stock Incentive Plans Recognized (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation expense:
Total Expense	$ 1,188	$ 1,016	$ 1,303
Tax benefit on nonqualified stock option expense and restricted stock awards	244	162	296
Stock Options [Member]
Stock-based compensation expense:
Total Expense	463	517	408
Restricted Stock Awards [Member]
Stock-based compensation expense:
Total Expense	679	461	859
Employee Stock Purchase Plan [Member]
Stock-based compensation expense:
Total Expense	$ 46	$ 38	$ 36