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Compensation and Other Benefit Plans - Additional Information (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2017 | May 31, 2017 | Feb. 28, 2017 | May 31, 2016 | Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Apr. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Maximum annual contribution per employee (in hundredths) |  |  |  |  |  | 50.00% |  |
Maximum annual contribution per employee |  |  |  |  |  | $ 18,500 | $ 18,000 |
Maximum annual contribution per employee over 50 years old |  |  |  |  |  | $ 24,500 | $ 24,000 |
Age requirement for participant to be eligible for a catch-up contribution, minimum |  |  |  |  |  | 50 years | 50 years |
Employer matching contribution percentage, maximum (in hundredths) |  |  |  |  |  | 50.00% |  |
Deferred savings plan expense |  |  |  |  |  | $ 100,000 | $ 0 |
Deferred savings plan expense paid in common shares (in hundredths) |  |  |  |  |  | 100.00% |  |
Number of shares of common stock to be issued upon exercise of options and RSUs outstanding (in shares) |  |  |  |  |  | 1,627,591 |  |
Stock-based compensation expense |  |  |  |  |  | $ 3,902,000 | 7,301,000 |
Non Executive Employee [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 3 years |  |
Non Executive Employee [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 4 years |  |
Directors [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 1 year |  |
Stock Options [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Minimum age required for employees to qualify for immediate vesting of RSUs |  |  |  |  |  | 55 years |  |
Threshold years required for retirement age |  |  |  |  |  | 70 years |  |
Number of stock options granted to members of board of directors, executives, and non-executive employees |  |  |  |  |  | 305,708 |  |
Options exercised, aggregate intrinsic value |  |  |  |  |  | $ 1,100,000 | $ 2,400,000 |
Weighted-average grant-date fair value |  |  |  |  |  | $ 18.25 | $ 10.26 |
Unrecognized compensation expense related to stock options |  |  |  |  |  | $ 5,000,000 |  |
Weighted average period of unrecognized compensation expense expected to be recognized |  |  |  |  |  | 1 year 9 months 18 days |  |
Performance Shares [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of options outstanding, non-vested options |  |  |  |  |  | 41,250 |  |
Number of options vested |  |  |  |  |  | 41,250 |  |
Stock-based compensation expense |  |  |  |  |  | $ 200,000 |  |
Grant date fair value |  |  |  |  |  | $ 200,000 |  |
Performance Shares [Member] | Executives [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of stock options granted to members of board of directors, executives, and non-executive employees | 130,000 |  |  |  |  |  |  |
Stock options cancelled |  |  |  |  | 50,000 |  |  |
Service-Based Stock Options [Member] | Executives [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of stock options granted to members of board of directors, executives, and non-executive employees |  |  |  |  | 80,000 |  |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Minimum age required for employees to qualify for immediate vesting of RSUs |  |  |  |  |  | 55 years |  |
Threshold years required for retirement age |  |  |  |  |  | 70 years |  |
Weighted average period of unrecognized compensation expense expected to be recognized |  |  |  |  |  | 9 months 18 days |  |
Total grant-date fair value of RSUs, vested |  |  |  |  |  | $ 300,000 | $ 2,300,000 |
Unrecognized compensation expense related to employee RSUs |  |  |  |  |  | $ 2,400 |  |
Restricted Stock Units (RSUs) [Member] | Non Executive Employee [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 3 years |  |
Restricted Stock Units (RSUs) [Member] | Directors [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Vesting period |  |  |  |  |  | 1 year |  |
2015 ESPP [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage related to employees to purchase shares at the lower fair market value at offering period |  |  |  |  |  | 85.00% |  |
Common stock reserved for future issuance (in shares) |  |  |  |  |  | 15,000 |  |
Percentage of compensation of eligible employees to purchase shares of entity common stock at discount through payroll deductions |  |  |  |  |  | 10.00% |  |
Shares purchased (in shares) |  |  |  |  |  | 2,948 | 5,314 |
2015 ESPP [Member] | Common Stock [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in aggregate number of shares authorized for issuance |  | 250,000 |  |  |  |  |  |
Shares authorized for issuance |  | 265,000 |  |  |  |  |  | 15,000
Increase in shares per person award limits |  | 2,500 |  |  |  |  |  |
2010 Plan [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in aggregate number of shares authorized for issuance |  |  |  | 170,000 |  |  |  |
Shares authorized for issuance |  |  |  | 1,108,560 |  |  |  |
Expiration period |  |  |  |  |  | ten years from the date of the grant or three to six months from the date of termination of employment (longer in case of death or certain retirements). |  |
Vesting period |  |  |  |  |  | 3 years |  |
Number of stock options granted to members of board of directors, executives, and non-executive employees |  | 998,000 | 1,018,000 |  |  |  |  |
2010 Plan [Member] | Options and Stock Appreciation Rights [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in shares per person award limits |  | 2,000,000 |  |  |  |  |  |
2010 Plan [Member] | Other Types of Stock Awards [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in shares per person award limits |  | 2,000,000 |  |  |  |  |  |
2010 Plan [Member] | Common Stock [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in aggregate number of shares authorized for issuance |  | 1,470,502 |  |  |  |  |  |
Shares authorized for issuance |  | 2,579,062 |  |  |  |  |  |
2010 Plan [Member] | Common Stock [Member] | Incentive Stock Options [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Increase in aggregate number of shares authorized for issuance |  | 2,004,087 |  |  |  |  |  |
Shares authorized for issuance |  | 2,579,062 |  |  |  |  |  |
Long Term Incentive Plan [Member] |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares available for grant |  |  |  |  |  | 341,540 |  |

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation. + References 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested options awarded to employees as compensation. + References 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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- Definition 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. + References 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition 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. + References No definition available. + Details
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- Definition The highest quantity of shares an employee can purchase under the plan per period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan. + References 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)(iv)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References 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 (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of shares purchased on the open market during the period for issuance to employees under the plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 + Details
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