Share-Based Compensation - Share-Based Compensation Amounts Included in Net Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense	$ 454	$ 385	$ 1,519	$ 1,246
Less: tax benefit	(183)	(155)	(612)	(502)
Share-Based Compensation amounts included in net income	271	230	907	744
Awards to non-employee directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense	137	124	394	354
Award to key employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense	$ 317	$ 261	$ 1,125	$ 892