Equity Compensation Plans (Narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) item shares	Mar. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based incentive plans \| item	2
Share-based compensation expense recognized \| $	$ 3,890	$ 3,628
Share-based compensation expense \| $	$ 3,890	$ 3,628
Participants purchase limit shares	3,000
Offering period	6 months
Minimum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Maximum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
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	10,249,000
Shares available for future grants	562,000
2014 Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period beginning	3 years
2008 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	225,000
Company's common stock may be purchased at a discount	15.00%
Participants purchase limit value \| $	$ 25
Shares available for sale under the ESPP increased	2.00%
Outstanding shares of common stock exceed	600,000
2018 PSAs [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting right of shares of common stock	1
Vesting period	3 years
2018 PSAs [Member] \| Minimum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	0.00%
2018 PSAs [Member] \| Maximum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance stock award threshold, target and maximum payout opportunity percentage	200.00%
2018 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	500,000
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%
First, Second, And Third Anniversaries [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	0.33%
First, Second, And Third Anniversaries [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	0.33%

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Exercisable period beginning.

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- Definition

Option one percentage of outstanding shares.

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Option two maximum number of shares.

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Performance stock award threshold, target and maximum payout opportunity percentage.

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- Definition

Share based compensation arrangement by share based payment award maximum value per employee.

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Number of share-based incentive plans.

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Vesting right of shares of common stock.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Number of common shares reserved for future issuance related to deferred compensation arrangements with individuals.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Discount rate from fair value on purchase date that participants pay for shares.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest quantity of shares an employee can purchase under the plan per period.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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