Accounting for Stock Based Compensation - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			228 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011 Director [Member]	Dec. 31, 2011 Minimum [Member] Employee [Member]	Dec. 31, 2011 Maximum [Member] Employee [Member]	Dec. 31, 2012 Equity Incentive Plan Twenty Eleven [Member]	May 10, 2012 Equity Incentive Plan Twenty Eleven [Member]	Dec. 31, 2012 Two Thousand Six Equity Incentive Plan [Member]	Dec. 31, 2011 Two Thousand Six Equity Incentive Plan [Member]	Dec. 31, 2011 Equity Incentive Plan Nineteen Ninety Seven [Member]	Dec. 31, 2011 Stock Incentive Plan Nineteen Ninety Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional number of shares authorized for grant									2,000,000
Number of shares authorized for grant								2,304,000		8,578
Expiration date of plan											2016-05	2007-04	2003-04
Stock options vesting period					1 year	3 years	5 years
Weighted average grant date fair value of options granted	$ 4.13	$ 4.78	$ 4.30
Total intrinsic value of options exercised	$ 1,663	$ 4,876	$ 3,404	$ 11,583
Unrecognized compensation cost related to nonvested options and restricted options	3,690	4,319		3,690
Unrecognized share-based compensation cost recognition period	2 years
Share-based compensation expense	$ 823	$ 1,403	$ 1,275