Computation of Basic and Diluted Net Income Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Numerator:
Net income	$ 1,081	$ 2,745	$ 4,505	$ 6,286	$ 4,256	$ 3,893	$ 5,525	$ 4,448	$ 14,617		$ 18,122		$ 13,242
Adjustment for interest expense on convertible notes, net of capitalized interest									458		119
Net income, as adjusted									$ 15,075		$ 18,241		$ 13,242
Denominator:
Weighted average number of shares of Common Stock outstanding									6,874,669		6,826,490		6,782,576
Weighted average effect of dilutive stock options and other stock compensation									151,223		153,397		85,679
Weighted average effect of assumed conversion of convertible notes									428,138	[1]	158,937	[1]
Weighted average number of shares of Common Stock outstanding, as adjusted									7,454,030		7,138,824		6,868,255
Net income per common share:
Net income per common share - Basic	$ 0.16	$ 0.40	$ 0.66	$ 0.92	$ 0.62	$ 0.57	$ 0.81	$ 0.65	$ 2.13		$ 2.65		$ 1.95
Net income per common share - Diluted	$ 0.16	$ 0.38	$ 0.62	$ 0.86	$ 0.59	$ 0.55	$ 0.79	$ 0.64	$ 2.02		$ 2.56		$ 1.93

[1] The weighted average for the assumed conversion of the Notes was calculated from the August 18, 2011 issuance.