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Income Taxes - Additional Information (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Tax [Line Items] |  |  |  |  |
Corporate federal income tax rate |  |  | 35.00% | 35.00% | 35.00%
Net income tax expense | $ 7,200,000 |  | $ 7,200,000 |  |
Reversal of valuation allowance |  |  |  | $ 61,400,000 |
Operating loss carryforwards, limitations on use |  |  | Pursuant to Sections 382 and 383 of the Internal Revenue Code, annual use of net operating loss and credit carryforwards may be limited in the event a cumulative change in ownership of more than 50 percent occurs within a three-year period. |  |
Cumulative change in ownership Percentage | 50.00% |  | 50.00% |  |
Period for cumulative change in ownership |  |  | 3 years |  |
Estimated net operating losses available eah year | $ 756,000 |  | $ 756,000 |  |
Scenario, Plan |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |
Corporate federal income tax rate |  | 21.00% |  |  |

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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319 + Details
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