Share Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended											12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Two Thousand Four Stock Incentive Plan	Mar. 31, 2012 Two Thousand Four Stock Incentive Plan	Mar. 31, 2013 Stock Options	Mar. 31, 2012 Stock Options	Mar. 31, 2013 Stock Options Awards That Contain Performance Or Market Conditions	Mar. 31, 2013 Restricted Stock	Mar. 31, 2012 Restricted Stock	Mar. 31, 2012 1998 ESPP	Mar. 31, 2013 1998 ESPP Minimum	Dec. 31, 2011 2011 Incentive Plan	Mar. 31, 2013 2011 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued upon exercise of outstanding stock options												7,750,000
Shares remain available for future grant													913,050
Stock compensation expense	$ 960,000	$ 1,218,000	$ 1,000,000	$ 1,200,000						$ 300,000
Stock option compensation cost charged against operations					600,000	1,300,000	26,000	600,000	700,000
Unrecognized compensation cost	3,400,000							3,400,000
Unamortized stock option compensation, expected to be recognized over a weighted-average period, years	2 years
Income as result of reversal of prior compensation expense		500,000
Options remain unvested		871,364						1,828,905
Shares of restricted stock issued								641,933
Total aggregate fair market value of restricted stock issued								600,000
Total fair value of restricted stock vested								$ 1,600,000	$ 1,100,000
Employee Stock Purchase Plan, purchase price											85.00%
Employee Stock Purchase Plan, purchase discount											5.00%