Significant Accounting Policies - Additional Information (Detail) - USD ($) shares in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016		Sep. 13, 2017	Feb. 25, 2015	Feb. 10, 2014	May 22, 2012
Significant Accounting Policies [Line Items]
Plan Effective Date	Mar. 19, 2012
Unearned premiums	$ 33,000		$ 270,000	[1]
Premium deficiency reserves	500,000		300,000
Other liabilities	13,774,000		14,063,000	[1]
Accrued professional fees	800,000
Comprehensive income	0
Amount of dividends paid on or after Effective Date	0
Preferred stock dividends declared	13,500,000		18,000,000
Preferred stock dividends paid	13,500,000	$ 13,500,000
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	12,300,000
Accrued dividends	700,000
Preferred stock dividends declared	13,500,000		18,000,000
Additional accrued preferred stock dividends	700,000		700,000
Preferred stock dividends paid	$ 13,500,000		$ 18,000,000
Preferred stock dividend rate	3.00%		3.00%
Distribution from WMMRC to WMIH Deposited in Collateral Account [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Approved amount for distribution					$ 10,700,000

[1] Balances derived from audited financial statements as of December 31, 2016.