Stock-based Compensation (Details) (USD $)	12 Months Ended																		0 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012 Stock options	Dec. 31, 2011 Stock options	Dec. 31, 2010 Stock options	Dec. 31, 2011 Stock options Vice president and above ranking other than executive officers	Dec. 31, 2011 Stock options Executive officers	Dec. 31, 2012 Incentive stock options Minimum	Dec. 31, 2012 Incentive stock options Maximum	Dec. 31, 2012 Nonstatutory stock options Minimum	Dec. 31, 2012 Nonstatutory stock options Outside directors	Dec. 31, 2012 Nonstatutory stock options Outside directors Minimum	Dec. 31, 2012 Nonstatutory stock options Outside directors Maximum	Dec. 31, 2011 Nonstatutory stock options Outside directors not initially elected at annual meeting	Dec. 31, 2012 Restricted stock units item	Dec. 31, 2011 Restricted stock units	Dec. 31, 2011 Restricted stock units Vice president and above ranking other than executive officers	Dec. 31, 2011 Restricted stock units Executive officers	Dec. 31, 2012 Restricted stock Outside directors	Dec. 31, 2011 Restricted stock Outside directors	Sep. 08, 2005 2005 Stock Incentive Plan	Dec. 31, 2012 2005 Stock Incentive Plan	Dec. 31, 2012 2001 Employee Stock Purchase Plan	Jun. 30, 2011 2001 Employee Stock Purchase Plan	Dec. 31, 2012 2001 Employee Stock Purchase Plan Minimum
Stock-based compensation
Shares reserved for issuance																			5,000,000			1,250,000
Increase in shares reserved for issuance																			3,980,000
Shares of common stock available for future grant																				2,211,387	1,103,937
Exercise price as a percentage of the fair market value of the company's stock						100.00%		80.00%	100.00%														85.00%
Term of incentive stock options from the date of grant							10 years				10 years
Vesting percentage at the end of the first year									25.00%
Vesting period, after the first anniversary, in which the options vest monthly									3 years
Number of equal annual installments													3
Vesting period												1 year
Term of stock options after termination of the outside directors' service										12 months
Target percentage of equity grant value				50.00%	75.00%										50.00%	25.00%
Maximum period for offerings under ESPP																					27 months
Purchase price as a percentage of fair market value per share, minimum						100.00%		80.00%	100.00%														85.00%
Length of purchase period under ESPP																					6 months
Number of shares issued under ESPP																					146,063
Unrecognized compensation expense																					$ 540,000
Weighted-average period of recognition of unrecognized stock-based compensation expense																					5 months
Number of Shares
Options outstanding at the beginning of the period (in shares)	5,027,000	5,322,000	4,684,000
Options granted (in shares)	608,000	561,000	1,265,000
Options exercised (in shares)	(958,000)	(748,000)	(327,000)
Options forfeited (in shares)	(154,000)	(108,000)	(300,000)
Options outstanding at the end of the period (in shares)	4,523,000	5,027,000	5,322,000
Exercisable at the end of the period (in shares)	3,422,000
Vested and expected to vest at the end of the period (in shares)	4,403,000
Weighted-Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$ 17.12	$ 15.88	$ 15.36
Options granted (in dollars per share)	$ 30.27	$ 23.40	$ 16.90
Options exercised (in dollars per share)	$ 16.03	$ 12.78	$ 9.13
Options forfeited (in dollars per share)	$ 25.20	$ 19.01	$ 19.35
Options outstanding at the end of the period (in dollars per share)	$ 18.84	$ 17.12	$ 15.88
Exercisable at the end of the period (in dollars per share)	$ 16.93
Vested and expected to vest at the end of the period (in dollars per share)	$ 18.64
Weighted-Average Remaining Contractual Life
Options outstanding at the end of the period	5 years 10 months 24 days
Exercisable at the end of the period	5 years 1 month 6 days
Vested and expected to vest at the end of the period	5 years 9 months 18 days
Aggregate Intrinsic Value
Options outstanding at the end of the period (in dollars)	39,603,000
Exercisable at the end of the period (in dollars)	35,285,000
Vested and expected to vest at the end of the period (in dollars)	39,257,000
Additional disclosure related to options
Intrinsic value (in dollars)	15,300,000	9,800,000	2,900,000
Fair value of shares vested (in dollars)	7,900,000	10,100,000	5,500,000
Number of Shares
Balance at the beginning of the period (in shares)													322,000
Granted (in shares)													435,000	338,000			5,512	5,278
Vested (in shares)													(111,000)
Cancelled (in shares)													(54,000)	(16,000)
Balance at the end of the period (in shares)													592,000	322,000
Weighted-Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)													$ 23.29
Granted (in dollars per share)													$ 29.81	$ 23.28			$ 30.79	$ 25.16
Vested (in dollars per share)													$ 23.37
Cancelled (in dollars per share)													$ 28.46	$ 23.06
Balance at the end of the period (in dollars per share)													$ 27.59	$ 23.29
Additional Disclosure
Fair value (in dollars)													3,300,000
Restricted Stock in Lieu of Directors' Fees
Granted (in shares)													435,000	338,000			5,512	5,278
Restricted stock units awarded, weighted-average grant-date fair value																	$ 172,000	$ 130,000
Weighted-average grant date fair value (in dollars per share)													$ 29.81	$ 23.28			$ 30.79	$ 25.16