Stockholders' Equity, Stock Plans (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2009 shares	Dec. 31, 2018 Installment $ / shares shares	Dec. 31, 2017 shares	May 31, 2017 shares	Apr. 30, 2017 shares	Jun. 30, 2015 shares	May 31, 2015 shares
Stock Options [Member]
Stock Plans [Abstract]
Number of options outstanding (in shares)		11,311,000	9,397,000
Number of options exercisable (in shares)		6,071,000
Restricted Stock Units [Member]
Stock Plans [Abstract]
Vesting period		4 years
1989 Stock Option Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)		20,000,000
Vesting period		4 years
Award term		7 years
Number of options outstanding (in shares)		848,753
Number of options exercisable (in shares)		831,656
Number of shares available for grant (in shares)		42,925
1989 Stock Option Plan [Member] | One Year from Date of Grant [Member]
Stock Plans [Abstract]
Vesting percentage		25.00%
2011 Equity Incentive Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)				16,000,000	11,000,000	11,000,000	5,500,000
Number of options outstanding (in shares)		9,705,441
Number of options exercisable (in shares)		4,801,904
Number of shares available for grant (in shares)		3,340,351
Period before change of control when vesting will accelerate for executive officers		3 months
Period after change of control when vesting will accelerate for executive officers		12 months
Number of awards outstanding (in shares)		1,183,154
2011 Equity Incentive Plan [Member] | Stock Options [Member] | Minimum [Member]
Stock Plans [Abstract]
Vesting period		2 years
2011 Equity Incentive Plan [Member] | Restricted Stock Units [Member]
Stock Plans [Abstract]
Vesting period		4 years
2011 Equity Incentive Plan [Member] | Restricted Stock Units [Member] | Minimum [Member]
Stock Plans [Abstract]
Vesting period		3 years
2002 Non-Employee Directors' Stock Option Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)						2,000,000	1,200,000
Award term		10 years
Number of options outstanding (in shares)		757,750
Number of options exercisable (in shares)		437,750
Number of shares available for grant (in shares)		420,762
Number of awards outstanding (in shares)		63,099
2002 Non-Employee Directors' Stock Option Plan [Member] | One Year from Date of Grant [Member]
Stock Plans [Abstract]
Number of equal annual installments over which options become exercisable | Installment		4
Employee Stock Purchase Plan [Member]
Stock Plans [Abstract]
Number of shares authorized (in shares)		3,674,596
Number of shares available for grant (in shares)		774,816
Number of additional shares reserved for issuance (in shares)	150,000	150,000
Maximum percentage of employee compensation used to purchase shares		10.00%
Percentage of fair market value used to determine purchase price of stock		85.00%
Purchase period		6 months
Holding period for purchased stock		6 months
Shares purchased and issued under ESPP (in shares)		43,416
Purchase price (in dollars per share) | $ / shares		$ 39.03