Preferred Stock and Stockholders' Equity (Narrative) (Details)		12 Months Ended			17 Months Ended
	Feb. 07, 2020 shares	Dec. 31, 2019 USD ($) stock_option_plan $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Aug. 09, 2018 USD ($)	Dec. 31, 2016 shares	Dec. 31, 2012 shares
Shareholders Equity [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000		10,000,000
Preferred stock, par value (in USD per share) | $ / shares		$ 0.001	$ 0.001		$ 0.001
Preferred stock, shares outstanding (in shares)		0	0		0
Increase in shares authorized for grant (in shares)		4,601,000	4,589,000	4,508,000
Number of stock option plans | stock_option_plan		2
Shares available for future grants (in shares)		8,624,000	7,726,000	7,630,000	8,624,000		7,920,000
Total intrinsic value of options exercised | $		$ 26,600,000	$ 26,600,000	$ 22,400,000
Fair value of options vested | $		$ 30,200,000	$ 22,600,000	$ 12,300,000
Stock options outstanding (in shares)		23,600,000	22,826,000	20,454,000	23,600,000		17,663,000
Aggregate purchase price | $		$ 30,975,000	$ 23,657,000
Shares issued in net-share settlement of cashless option exercises (in shares)		1,200,000	0	0
Employee and Director Stock Option
Shareholders Equity [Line Items]
Non-cash stock-based compensation expense | $		$ 29,200,000	$ 23,800,000	$ 13,400,000
Unrecognized compensation expense | $		$ 55,000,000.0			$ 55,000,000.0
Unrecognized compensation expense, weighted-average vesting period		2 years 5 months 23 days
Non-employee
Shareholders Equity [Line Items]
Stock options outstanding (in shares)		0			0
2012 Equity Incentive Award Plan
Shareholders Equity [Line Items]
Increase in shares available for issuance based on percentage of common stock outstanding		4.00%			4.00%
Exercise price as percentage of fair value of common stock, no less than		100.00%
Shares available for future grants (in shares)								5,300,000
2012 Equity Incentive Award Plan | Minimum
Shareholders Equity [Line Items]
Stock options, vesting period		1 year
2012 Equity Incentive Award Plan | Maximum
Shareholders Equity [Line Items]
Stock options, vesting period		4 years
2004 Equity Incentive Plan
Shareholders Equity [Line Items]
Exercise price as percentage of fair value of common stock, no less than		100.00%
Shares available for future grants (in shares)								0
2004 Equity Incentive Plan | Minimum
Shareholders Equity [Line Items]
Stock options, vesting period		1 year
2004 Equity Incentive Plan | Maximum
Shareholders Equity [Line Items]
Stock options, vesting period		5 years
Common Stock | Stock Repurchase Program
Shareholders Equity [Line Items]
Authorized amount | $						$ 100,000,000
Shares repurchased (in shares)		2,800,000			4,600,000
Aggregate purchase price | $		$ 31,000,000.0			$ 54,600,000
Cost per share (in dollars per share) | $ / shares		$ 11.14			$ 11.91
Non-employee
Shareholders Equity [Line Items]
Non-cash stock-based compensation expense | $		$ 200,000	$ 0	$ 0
Common Stock
Shareholders Equity [Line Items]
Shares repurchased (in shares)		2,780,000	1,807,000
Shares tendered to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises (in shares)		631,000
Subsequent event | 2012 Equity Incentive Award Plan
Shareholders Equity [Line Items]
Increase in shares authorized for grant (in shares)	4,600,000