Employee Stock and Benefit Plans (Common Stock and Preferred Stock) (Details) - $ / shares	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 03, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	3,429,309		4,495,891	7,527,680	7,579,058
Total shares reserved for future issuance	8,539,466
Preferred Stock
Preferred stock, shares authorized		20,000,000	20,000,000
Preferred stock, par value per share (in dollars per share)		$ 0.001	$ 0.001
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Preferred Stock
Preferred Stock
Preferred stock, shares authorized						20,000,000
Preferred stock, par value per share (in dollars per share)						$ 0.001
2000 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	244,652
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options and RSUs outstanding under equity incentive plans	4,477,717
Shares available for future grants under an equity incentive plan	3,817,097