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Equity Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2014 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Total intrinsic value of options exercised |  | $ 5,121 | $ 3,550 | $ 2,740
Tax benefit recognized |  | 0 | 0 | 0
Share-based compensation expense recognized |  | 14,615 | 11,697 | 8,997
Unrecognized compensation costs related to non-vested share-based compensation arrangements with performance shares |  | 23,331 |  |
Share-based compensation expense |  | $ 14,615 | 11,697 | 8,997
Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average period of recognizing cost |  | 2 years 2 months 12 days |  |
Stock options compensation costs |  | $ 2,197 |  |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Weighted average period of recognizing cost |  | 2 years 2 months 12 days |  |
Total fair value of restricted stock vested |  | $ 6,235 | $ 5,102 | 2,767
Unrecognized compensation costs related to non-vested performance options |  | $ 21,134 |  |
Performance options awarded to President and CEO |  | 771 | 710 |
Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Expiry of options from the date of grant |  | 10 years |  |
Share-based compensation expense |  | $ 43 | $ 269 | 546
Performance options awarded to President and CEO | 450 |  |  |
Number of shares options vest in |  | 25 |  |
Period of considering closing price of common stock |  | 30 days |  |
Contractual term (years) |  | 10 years |  |
Stock Options And Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation expense recognized |  | $ 13,908 | $ 10,872 | $ 8,072
Minimum [Member] | Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Contractual term (years) |  | 5 years 2 months 16 days | 5 years 3 months 7 days | 5 years 2 months 12 days
Expected volatility of stock |  | 43.00% | 46.00% | 46.00%
Interest rate |  | 1.75% | 1.06% | 1.30%
Minimum [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Strike price |  | $ 5.91 |  |
Expected volatility of stock |  | 60.50% |  |
Interest rate |  | 1.75% |  |
Maximum [Member] | Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Contractual term (years) |  | 5 years 9 months 4 days | 7 years 1 month 6 days | 6 years 10 months 21 days
Expected volatility of stock |  | 48.00% | 51.00% | 67.00%
Interest rate |  | 2.12% | 2.02% | 1.96%
Maximum [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Strike price |  | $ 21.04 |  |
Expected volatility of stock |  | 69.60% |  |
Interest rate |  | 2.73% |  |
2014 Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Expiry of options from the date of grant |  | 10 years |  |
Common stock reserved for issuance |  | 10,249 |  |
Shares available for future grants |  | 1,128 |  |
2014 Plan [Member] | Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Exercisable period beginning |  | 3 years |  |
2014 Plan [Member] | Minimum [Member] | Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 1 year |  |
2014 Plan [Member] | Maximum [Member] | Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period |  | 4 years |  |
2008 Employee Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation expense recognized |  | $ 664 | $ 556 | $ 379
Company's common stock may be purchased at a discount |  | 15.00% |  |
Participants purchase limit value |  | $ 25 |  |
Description of participants purchase limit |  | Participants may not purchase more than $25 of the Company's common stock in a calendar year and may not purchase a value of more than 3 shares during an offering period. |  |
Participants purchase limit shares |  | 3 |  |
Offering period |  | 6 months |  |
Shares available for sale under the ESPP increased |  | 2.00% |  |
Outstanding shares of common stock exceed |  | 600 |  |
Shares available for future issuance under the ESPP |  | 225 |  |
First Anniversary Date Of Grant [Member] | 2014 Plan [Member] | Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Annual vesting percentage |  | 25.00% |  |
Tranche 4 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | $ 17.50 |  |
Tranche 5 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | 20.00 |  |
Tranche 6 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | 25.00 |  |
Tranche 7 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | 30.00 |  |
Tranche 8 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | 35.00 |  |
Tranche 9 [Member] | Performance Stock Options [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Price by which volume adjusted weighted average closing price exceeds under vesting condition |  | $ 40.00 |  |

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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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