Stock Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended		12 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Employee Stock Purchase Plan	Jun. 30, 2011 Employee Stock Purchase Plan	Jun. 30, 2012 Employee Stock Purchase Plan	Jun. 30, 2011 Employee Stock Purchase Plan	Mar. 31, 2012 Stock Options	Jun. 30, 2012 Stock Options	Jun. 30, 2012 Stock Options Maximum	Jun. 30, 2012 Performance-Based Restricted Stock	Jun. 30, 2011 Performance-Based Restricted Stock	Jun. 30, 2012 Performance-Based Restricted Stock	Jun. 30, 2011 Performance-Based Restricted Stock	Dec. 31, 2010 Performance-Based Restricted Stock	Dec. 31, 2011 Performance-Based Restricted Stock	Dec. 31, 2010 Performance-Based Restricted Stock Maximum	Dec. 31, 2010 Performance-Based Restricted Stock Minimum	Jun. 30, 2012 Time Based Restricted Stock	Jun. 30, 2011 Time Based Restricted Stock	Jun. 30, 2012 Time Based Restricted Stock	Jun. 30, 2011 Time Based Restricted Stock	Jun. 30, 2012 Deferred Stock Units	Jun. 30, 2011 Deferred Stock Units	Jun. 30, 2012 Deferred Stock Units	Jun. 30, 2011 Deferred Stock Units	Jun. 30, 2012 Stock Option	Jun. 30, 2011 Stock Option	Jun. 30, 2012 Stock Option	Jun. 30, 2011 Stock Option
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock options, contractual term											10 years
Stock options, expected dividend yield										0.00%
Stock-based compensation, approximate forfeitures rate									3.00%
Compensation expense			$ 2,678,000	$ 3,610,000	$ 100,000	$ 100,000	$ 200,000	$ 200,000				$ 500,000	$ 900,000	$ 400,000	$ 1,100,000					$ 400,000	$ 200,000	$ 900,000	$ 200,000	$ 700,000	$ 700,000	$ 700,000	$ 700,000	$ 600,000	$ 800,000	$ 1,300,000	$ 1,300,000
Options exercised, total intrinsic value			1,100,000
Total amount of cash received from exercise of options			$ 3,500,000
Restricted stock award program, measurement period																3 years
Restricted stock award program, awarded shares as a percentage of the original award amount																		200.00%	0.00%
Restricted stock award program, payment of award as percentage of target																	97.40%
Restricted stock award program, vesting period																						3 years
Employee stock purchase plan, purchase price discount							15.00%
Employee stock purchase plan, number of offering			2
Employee stock purchase plan, offering period			6 months