Stock-Based Compensation Plans - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended				1 Months Ended		1 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended					1 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended			3 Months Ended		12 Months Ended									3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2007	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jul. 24, 2007	Aug. 31, 2001 Share Exchange Person	Aug. 01, 2001 Share Exchange	Aug. 31, 2001 Share Exchange Minimum	Aug. 31, 2001 Share Exchange Maximum	Dec. 31, 2011 Employee Stock Purchase Plan 1999	Dec. 31, 2010 Employee Stock Purchase Plan 1999	Dec. 31, 2009 Employee Stock Purchase Plan 1999	Jul. 24, 2007 2005 Stock Incentive Plan	Dec. 31, 2011 Restricted share awards (RSAs)	Dec. 31, 2010 Restricted share awards (RSAs)	Dec. 31, 2009 Restricted share awards (RSAs)	Dec. 31, 2011 Restricted share awards (RSAs) Minimum	Dec. 31, 2011 Restricted share awards (RSAs) Maximum	Aug. 31, 2001 Replacement stock options Share Exchange	Aug. 01, 2001 Replacement stock options Share Exchange	Dec. 31, 2011 1994 Stock Option Plan Year	Aug. 31, 2001 1994 Stock Option Plan Share Exchange	Dec. 31, 2011 2002 Non-Employee Director Stock Option Plan Year	Dec. 31, 2011 1999 Stock Option Plan Year	Dec. 31, 2011 1996 Stock Option Plan Year	Dec. 31, 2011 LTIP Performance Shares	Dec. 31, 2008 LTIP Performance Shares	Dec. 31, 2011 LTIP Performance Shares Year	Dec. 31, 2010 LTIP Performance Shares	Dec. 31, 2009 LTIP Performance Shares	Sep. 30, 2008 LTIP Performance Shares	Sep. 30, 2007 LTIP Performance Shares	Dec. 31, 2011 LTIP Performance Shares Minimum	Dec. 31, 2010 LTIP Performance Shares Minimum	Dec. 31, 2009 LTIP Performance Shares Minimum	Sep. 30, 2007 LTIP Performance Shares Maximum	Dec. 31, 2011 LTIP Performance Shares 2009 Grant	Dec. 31, 2010 LTIP Performance Shares 2009 Grant	Dec. 31, 2011 LTIP Performance Shares 2010 Grant	Dec. 31, 2010 LTIP Performance Shares 2010 Grant	Dec. 31, 2011 LTIP Performance Shares 2011 Grant	Dec. 31, 2011 Stock Options Year	Dec. 31, 2011 Restricted Stock Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option plan expiration date																					2005-03-31		2005-03-31	2009-02-28	2005-03-31
Employee stock purchase plan, amended plan start date					May 01, 2008
Shares of common stock reserved for issuance										1,500,000			5,000,000								1,910,976		250,000	4,000,000	1,008,000
Employee stock purchase plan, amended plan end date					Apr. 30, 2018
Term of outstanding options																					10		10	10	10
Employee participating annual base compensation designated for purchase of common stock, amount										$ 25,000
Shares of common stock reserved for issuance prior to amendment													3,000,000
Stock option vesting period, minimum																								P3Y
Employee participating annual base compensation designated for purchase of common stock, Percentage										10.00%
Stock option vesting period																					4 years				4 years
Stock option vesting period, maximum																								P4Y
Price of common stock purchased under the ESPP, Percentage										85.00%
Employee Stock Purchase Plan Term	10 years												10 years
Shares issued under the ESPP		40,669	57,734	77,011
Incentive plan, weighted-average grant date fair value of stock options granted		$ 14.00	$ 12.22	$ 8.59
Incentive plan, total intrinsic value of stock options exercised		6,700,000	1,900,000	800,000
Proceeds from exercises of stock options		4,478,000	3,147,000	1,811,000
Actual tax benefit realized for the tax deductions from option exercises		2,500,000	700,000	300,000
Discount offered pursuant to ESPP, Percentage										15.00%
Stock-based compensation expense		11,254,000	7,790,000	7,645,000						200,000	200,000	200,000
Stock-based compensation expenses tax benefits		4,100,000	2,900,000	3,000,000
Total shares of common stock to be exchanged under the exchange program							3,089,100													1,823,000
Restricted Share Awards, vesting increments on the anniversary dates of grants														33.00%	33.00%	25.00%	25.00%	33.00%				25.00%
Exercise prices of options to acquire shares of common stock																			$ 10.04
Awards granted requisite service period														3 years	3 years	4 years	3 years	4 years	18 months
Exercise prices of options to acquire shares of common stock								$ 2.50	$ 45.00
Stock option exchange offer expiration date							Aug. 28, 2001
Number of shares cancelled under option		26,591	106,625	125,606		1,946,550
Number of employees whose shares were cancelled under option						578
Incentive plan, percentage of options expected to vest over the vesting period		94.40%
LTIP Performance Shares, Performance period																												3 years	3 years	3 years		3 years	1 year	1 year	1 year
Expected attainment level for the awards granted, percentage																											0.00%				100.00%					150.00%	200.00%	150.00%	175.00%	100.00%	100.00%
Maximum attainment percentage that may be achieved for LTIP Performance Shares																										200.00%		200.00%	200.00%	200.00%
Additional compensation expense due to revision of expected attainment level for the awards granted																										2,200,000
Restricted shares awards, shares vested														86,325	95,014	115,602
Restricted shares withheld to pay employees' portion of minimum payroll withholding taxes														25,495	30,304	38,167
Unrecognized compensation costs																										$ 13,300,000		$ 13,300,000														$ 7,500,000	$ 1,000,000
Unrecognized compensation costs, weighted-average recognition periods																												2.3														2.2	1.4