Income Taxes - Additional Information (Detail) - USD ($) |
3 Months Ended | 12 Months Ended | |||
---|---|---|---|---|---|
Mar. 31, 2018 |
Dec. 31, 2017 |
Mar. 31, 2018 |
Mar. 31, 2017 |
Mar. 31, 2016 |
|
Income Tax [Line Items] | |||||
Uncertain tax positions | $ 0 | $ 0 | $ 0 | $ 0 | |
Federal corporate tax rate | 21.00% | 31.55% | |||
Provisional benefit for re-measurement of deferred tax liabilities | $ 61,000,000 | ||||
Additional benefit due to re-measurement of deferred tax liabilities | $ 700,000 | ||||
Total benefit due to re-measurement of deferred tax liabilities | $ 61,700,000 | ||||
State Income Tax [Member] | |||||
Income Tax [Line Items] | |||||
Net operating loss carryforward | 1,500,000 | 1,500,000 | |||
Investment credits | $ 14,900,000 | $ 14,900,000 |