Share Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued upon exercise of outstanding stock options				33,000
Stock compensation expense			$ 5,165,000	$ 5,651,000
Proceeds from exercise of outstanding stock options				200,000
Unrecognized compensation cost	3,600,000		3,600,000
Unamortized stock option compensation, expected to be recognized over a weighted-average period, years		2 years 3 months 18 days
Income as a result of reversal of previously recorded compensation expense			700,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option compensation cost charged against operations	300,000	700,000	3,500,000	2,300,000
Compensation expense related to vesting of stock option awards	1,000	200,000	500,000
Stock Options That Contain Performance And Market-Based Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option compensation cost charged against operations				400,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	4,300,000		4,300,000
Shares of restricted stock issued	242,000	105,000	1,839,000	865,000
Total aggregate fair market value of restricted stock issued	400,000	600,000	3,400,000	7,100,000
Deferred restricted stock compensation cost charged against income	700,000	800,000	2,000,000	2,000,000
Number of shares remained unvested	1,991,000		1,991,000
Grant date fair value of restricted shares vested			2,100,000	1,700,000
Stock Options Awards That Contain Performance Or Market Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense		300,000		400,000
1998 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	100,000	200,000	800,000	500,000
1998 ESPP | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Purchase Plan, purchase price			85.00%
Employee Stock Purchase Plan, purchase discount			5.00%
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	2,838,764		2,838,764
Stock compensation expense	1,185,000	2,106,000	5,165,000	5,651,000
Stock Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 1,200,000	$ 2,100,000	$ 5,200,000	$ 5,700,000