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Stock-Based Compensation - Options by exercise price (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Stock options outstanding and exercisable by exercise price
Stock Options Outstanding, Number of Shares | shares	5,093,442
Stock Options Outstanding, Remaining Contractual Term	7 years 7 months 13 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 15.32
Stock Options Exercisable, Number of Shares | shares	2,558,941
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 11.06
$0.59 - $4.25
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	0.59
Range of Exercise Prices, upper limit (in dollars per share)	$ 4.25
Stock Options Outstanding, Number of Shares | shares	622,046
Stock Options Outstanding, Remaining Contractual Term	4 years 9 months 26 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 3.17
Stock Options Exercisable, Number of Shares | shares	622,046
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 3.17
$9.26 - $13.89
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	9.26
Range of Exercise Prices, upper limit (in dollars per share)	$ 13.89
Stock Options Outstanding, Number of Shares | shares	1,781,232
Stock Options Outstanding, Remaining Contractual Term	7 years 3 months 4 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 11.87
Stock Options Exercisable, Number of Shares | shares	1,205,142
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 11.64
$14.10 – $21.15
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	14.10
Range of Exercise Prices, upper limit (in dollars per share)	$ 21.15
Stock Options Outstanding, Number of Shares | shares	968,314
Stock Options Outstanding, Remaining Contractual Term	7 years 4 months 24 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 15.80
Stock Options Exercisable, Number of Shares | shares	634,199
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 15.68
$21.28 – $26.76
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	21.28
Range of Exercise Prices, upper limit (in dollars per share)	$ 26.76
Stock Options Outstanding, Number of Shares | shares	1,721,850
Stock Options Outstanding, Remaining Contractual Term	9 years 1 month 17 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 23.00
Stock Options Exercisable, Number of Shares | shares	97,554
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 24.13

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No definition available.

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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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