Share-Based Compensation - Exercise Prices (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding at end of year (in shares)	1,486,823	1,608,646
Wgtd. Avg. Remaining Contractual Life	7 years 11 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 6.34	$ 6.20
Options exercisable (in shares)	1,047,590
Wgtd. Avg. Exercise Price (usd per share)	$ 7.78
$0.00-$2.37
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	0
Exercise price range, upper range limit	$ 2.37
Outstanding at end of year (in shares)	250,477
Wgtd. Avg. Remaining Contractual Life	8 years 5 months 5 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 1.99
Options exercisable (in shares)	105,780
Wgtd. Avg. Exercise Price (usd per share)	$ 2.07
$3.17-$4.36
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	3.17
Exercise price range, upper range limit	$ 4.36
Outstanding at end of year (in shares)	1,013,663
Wgtd. Avg. Remaining Contractual Life	7 years 8 months 5 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 3.37
Options exercisable (in shares)	719,127
Wgtd. Avg. Exercise Price (usd per share)	$ 3.36
$16.72-$19.52
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	16.72
Exercise price range, upper range limit	$ 19.52
Outstanding at end of year (in shares)	68,190
Wgtd. Avg. Remaining Contractual Life	4 years 5 months 1 day
Wgtd. Avg. Exercise Price (in dollars per share)	$ 17.11
Options exercisable (in shares)	68,190
Wgtd. Avg. Exercise Price (usd per share)	$ 17.11
$20.40-$30.32
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	20.40
Exercise price range, upper range limit	$ 30.32
Outstanding at end of year (in shares)	154,493
Wgtd. Avg. Remaining Contractual Life	1 year 8 months 23 days
Wgtd. Avg. Exercise Price (in dollars per share)	$ 28.15
Options exercisable (in shares)	154,493
Wgtd. Avg. Exercise Price (usd per share)	$ 28.15

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
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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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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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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.

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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.

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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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