Stockholders' Equity (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Incentive Stock Option [Member]	Jun. 30, 2014 1998 Plan [Member] Incentive Stock Option [Member] Maximum [Member]	Jun. 30, 2014 2000 Plan [Member] Incentive Stock Option [Member]	Jun. 30, 2014 1998 and 2000 Plan [Member] Incentive Stock Option [Member]	Jun. 30, 2014 2009 Plan [Member] Incentive Stock Option [Member]	Jun. 30, 2014 2010 Employee Stock Purchase Plan [Member]	Jun. 30, 2010 2010 Employee Stock Purchase Plan [Member]	Jun. 30, 2014 2009 Plan [Member] Incentive Stock Option [Member]	Jun. 30, 2014 2012 Stock Repurchase Program [Member]	Mar. 13, 2014 2012 Stock Repurchase Program [Member]	Dec. 10, 2012 2012 Stock Repurchase Program [Member]	Jul. 23, 2014 Subsequent Event [Member] 2012 Stock Repurchase Program [Member]
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common Stock, Shares Authorized	100,000,000		100,000,000		100,000,000
Common stock, shares issued (in shares)	54,297,797		54,297,797		54,484,760
Common stock, shares outstanding (in shares)	54,297,797		54,297,797		54,484,760
Common stock, par value (in dollars per share)	$ 0.001		$ 0.001		$ 0.001
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock, Shares Authorized	5,000,000		5,000,000		5,000,000
Preferred stock, shares issued (in shares)	0		0		0
Preferred stock, shares outstanding (in shares)	0		0		0
Preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001		$ 0.001
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of stock options granted	$ 4.76	$ 5.72	$ 5.06	$ 6.16
Dividend yield	0.00%	0.00%	0.00%	0.00%
Shares of common stock available for issuance							5,850,000		10,000,000	14,300,000	615,000	1,000,000	23,817,744
Increase in number of shares of common stock available for issuance								4,150,000		6,000,000			4,250,000
Stock option term			10 years
Unrecognized compensation cost related to nonvested share-based compensation arrangements						$ 33,700,000
Weighted average recognition period of unrecognized compensation cost						2 years
Total value of stock options exercised			1,000,000
Total intrinsic value of options exercisable	12,300,000		12,300,000
Total intrinsic value of nonvested options	1,700,000		1,700,000
Total intrinsic value of all outstanding options	14,000,000		14,000,000
Stock repurchase program, authorized amount															40,000,000.0	30,000,000.0	50,000,000.0
Stock repurchased during period, shares														1,113,701
Treasury Stock, Shares	462,912		462,912
Stock repurchase program, remaining authorized repurchase amount														$ 1,100,000