Stockholders' Equity - Stock Option Activities of Stock Option Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Qualified Stock Option Plans [Member]
Stockholders Equity [Line Items]
Shares outstanding at beginning of year	516,330
Granted, Shares
Exercised, Shares	(31,880)
Cancelled/surrendered , forfeited or expired, Shares	(5,535)
Shares outstanding at end of year	478,915	516,330
Shares exercisable at end of year	154,040
Outstanding at beginning of year, Weighted-Average Exercise Price	$ 21.34
Granted, Weighted-Average Exercise Price
Exercised, Weighted-Average Exercise Price	$ 9.39
Cancelled/surrendered, forfeited or expired, Weighted-Average Exercise Price	$ 9.36
Outstanding at end of year, Weighted-Average Exercise Price	$ 22.28	$ 21.34
Exercisable at end of year, Weighted-Average Exercise Price	$ 15.73
Weighted-average fair value per option granted during year		$ 16.00
Total intrinsic value of options exercised during the year	$ 895,000	$ 3,294,000	$ 441,000
Total fair value of options vested during the year	861,000	208,000	214,000
Non-Qualified Stock Option Plans [Member]
Stockholders Equity [Line Items]
Shares outstanding at beginning of year	316,525
Granted, Shares
Exercised, Shares	(58,475)
Shares outstanding at end of year	258,050	316,525
Shares exercisable at end of year	60,275
Outstanding at beginning of year, Weighted-Average Exercise Price	$ 8.41
Granted, Weighted-Average Exercise Price
Exercised, Weighted-Average Exercise Price	$ 8.00
Outstanding at end of year, Weighted-Average Exercise Price	$ 8.50	$ 8.41
Exercisable at end of year, Weighted-Average Exercise Price	$ 8.32
Weighted-average fair value per option granted during year		$ 16.25
Total intrinsic value of options exercised during the year	1,574,000	2,110,000	805,000
Total fair value of options vested during the year	$ 731,000	$ 730,000	$ 721,000
2008 Plan [Member]
Stockholders Equity [Line Items]
Maximum number of securities for issuance	1,000,000
Number of awards available to be granted	349,905
Shares outstanding at end of year	467,915
Shares exercisable at end of year	143,040
1998 Plan [Member]
Stockholders Equity [Line Items]
Shares outstanding at end of year	11,000
Shares exercisable at end of year	11,000