Significant Accounting Policies - Additional Information (Detail) - USD ($) shares in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017		Feb. 25, 2015	Feb. 10, 2014	May 22, 2012
Significant Accounting Policies [Line Items]
Plan Effective Date	Mar. 19, 2012
Unearned premiums	$ 0		$ 39,000	[1]
Premium deficiency reserves	400,000		300,000
Other liabilities	16,893,000		16,303,000	[1]
Accrued professional fees	8,600,000		$ 4,700,000
Comprehensive income	$ 0
Income tax at the federal statutory rate	21.00%		35.00%
Amount of dividends paid on or after Effective Date	$ 0
Preferred stock dividends paid	1,000,000	$ 4,500,000
2012 Plan [Member]
Significant Accounting Policies [Line Items]
Common stock reserved for future issuance					12.0	3.0	2.0
Redeemable Convertible Series B Preferred Stock [Member]
Significant Accounting Policies [Line Items]
Accrued fees	8,300,000		$ 8,300,000
Accrued fees for extension of escrow agreement			2,500,000
Accrued cash dividends			800,000
Additional accrued preferred stock dividends	0		800,000
Preferred stock dividends paid	$ 1,000,000		$ 18,000,000

[1] Balances derived from audited financial statements as of December 31, 2017.