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Stock-Based Compensation - Plan details (Details)			12 Months Ended
	Jan. 01, 2018 shares	Jan. 01, 2014 shares	Dec. 31, 2018 item $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 shares
Stock options
Stock-based compensation
Total number of shares of common stock available for issuance			3,576,574	3,394,691	2,943,216
Options granted (in shares)			1,805,937	1,511,100
Information with respect to stock options outstanding
Exercisable options (in shares)			3,058,659	2,558,941	1,743,765
Weighted-average exercise price per share of exercisable options (in dollars per share) | $ / shares			$ 15.12	$ 11.06	$ 8.87
Weighted average grant date fair value per share of options granted during the year (in dollars per share) | $ / shares			$ 18.06	$ 16.92	$ 10.30
Weighted-average remaining contractual life			7 years 6 months 4 days	7 years 7 months 13 days	7 years 9 months 26 days
ESPP
Stock-based compensation
Total number of shares of common stock available for issuance			581,286
Initial term of plan			2 years
Second term of plan			2 years
Number of six month purchase periods | item			4
Purchase period			6 months
Increase in shares of common stock available for issuance (in shares)		313,545	0	0	0	0
Awards issued under the plan (in shares)			349,716
ESPP | Minimum
Stock-based compensation
Percentage of compensation that employees may withhold to purchase stock at a discount			1.00%
ESPP | Maximum
Stock-based compensation
Percentage of compensation that employees may withhold to purchase stock at a discount			15.00%
Purchase price as percentage of stock price at the initial offering date			85.00%
Purchase price as percentage of stock price at the purchase date			85.00%
Annual percentage increase in shares of common stock available for issuance			1.00%
Annual increase in shares of common stock available for issuance (in shares)			621,814
Restricted stock units
Stock-based compensation
Restricted stock granted (in shares)			33,933
Annual installment vesting periods | item			3
The 2010 Plan
Stock-based compensation
Total number of shares of common stock available for issuance			0
The 2013 Plan
Stock-based compensation
Total number of shares of common stock available for issuance			9,581,833
Annual percentage increase in shares of common stock available for issuance			4.00%
Increase in shares of common stock available for issuance (in shares)	1,880,100
Awards issued under the plan (in shares)			6,751,287

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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