Stockholders' Equity (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Jul. 23, 2014	Mar. 13, 2014	Dec. 10, 2012	Jun. 30, 2010
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)	57,143,697		57,143,697		56,701,331
Common stock, shares outstanding (in shares)	54,584,170		54,584,170		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]
Total intrinsic value of nonvested options	$ 400,000		$ 400,000
Treasury Stock, Shares	81,360		81,360
Granted	$ 4.20	$ 4.76	$ 4.54	$ 5.06
Dividend yield	0.00%	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	5 years	5 years	5 years	5 years
Share-based Compensation Arrangement By Share-based Payment Award, Fair Value Assumptions, Period Used To Determine Volatility			5 years
Stock option term			10 years
Total value of stock options exercised			$ 1,300,000
Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested share-based compensation arrangements	$ 21,900,000		$ 21,900,000
Weighted average recognition period of unrecognized compensation cost			2 years 6 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested share-based compensation arrangements	$ 12,000,000		$ 12,000,000
Weighted average recognition period of unrecognized compensation cost			3 years 8 months 12 days
Vesting period			4 years
1998 Plan [Member] | Incentive Stock Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance	5,850,000		5,850,000
2000 Plan [Member] | Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares of common stock available for issuance			4,150,000
1998 and 2000 Plan [Member] | Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance	10,000,000		10,000,000
2009 Plan [Member] | Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance	13,060,000		13,060,000
Increase in number of shares of common stock available for issuance			6,000,000
2010 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance	470,000		470,000						1,000,000
2009 Plan [Member] | 2009 Plan [Member] | Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance	23,817,744		23,817,744
Increase in number of shares of common stock available for issuance			4,250,000
2012 Stock Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount						$ 50,000,000.0	$ 40,000,000.0	$ 30,000,000.0
Stock repurchased during period, shares			224,172
Stock repurchase program, remaining authorized repurchase amount	$ 7,800,000		$ 7,800,000