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Stock-based Compensation - Additional Information (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Dec. 31, 2017 | Jun. 30, 2018 | Mar. 31, 2018 | Jun. 30, 2018 | Jun. 30, 2017
Additional disclosures [Abstract] |  |  |  |  |
Stock-based compensation expense |  |  |  | $ 2,186,000 | $ 2,855,000
Stock Options [Member] |  |  |  |  |
Additional disclosures [Abstract] |  |  |  |  |
Minimum age required for employees to qualify for immediate vesting of RSUs |  |  |  | 55 years |
Threshold years required for retirement age |  |  |  | 70 years |
Unrecognized compensation expense related to stock options |  | $ 6,400,000 |  | $ 6,400,000 |
Weighted average period of unrecognized compensation expense expected to be recognized |  |  |  | 2 years |
Options outstanding | 1,622,065 | 1,607,932 |  | 1,607,932 |
Options granted |  |  |  | 233,208 |
Performance Shares [Member] |  |  |  |  |
Additional disclosures [Abstract] |  |  |  |  |
Unrecognized compensation expense related to stock options |  | $ 300,000 |  | $ 300,000 |
Options outstanding |  | 82,500 |  | 82,500 |
Number of options subject to achievement of corporate goals |  | 41,250 |  | 41,250 |
Stock-based compensation expense |  | $ 55,000 |  | $ 100,000 |
Grant date fair value |  | 400,000 |  | $ 400,000 |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Additional disclosures [Abstract] |  |  |  |  |
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 |  |  |  | 1 year 3 months 18 days |
Unrecognized compensation expense related to employee RSUs |  | $ 4,000 |  | $ 4,000 |
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 |
Non Executive Employee [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  |  | 3 years |
Directors [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  |  | 1 year |
Directors [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  |  | 1 year |
Executives [Member] | Performance Shares [Member] |  |  |  |  |
Additional disclosures [Abstract] |  |  |  |  |
Options granted | 130,000 |  |  |  |
Stock options cancelled |  |  | 50,000 |  |
Executives [Member] | Service-Based Stock Options [Member] |  |  |  |  |
Additional disclosures [Abstract] |  |  |  |  |
Options granted |  |  | 80,000 |  |
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% |

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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 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 Number of options outstanding, including both vested and non-vested options. + 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 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Minimum age required for employees to qualify for immediate vesting of RSUs. + References No definition available. + Details
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