Capital Stock and Derivative Instruments - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		12 Months Ended
	Jun. 01, 2017	Jan. 05, 2015	Mar. 19, 2012	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017		Feb. 12, 2018	Jan. 05, 2018	Dec. 07, 2017	Dec. 31, 2016	Jun. 01, 2016	May 15, 2015	May 11, 2015	Jan. 30, 2014
Capital Stock Distribution [Line Items]
Common stock, shares authorized			500,000,000	3,500,000,000		3,500,000,000								3,500,000,000
Preferred stock, shares authorized			5,000,000	10,000,000										10,000,000
Common stock, par value			$ 0.00001	$ 0.00001		$ 0.00001								$ 0.00001
Preferred stock, par value			$ 0.00001	$ 0.00001										$ 0.00001
Conversion of shares														1
Warrants to purchase in aggregate, shares															61,400,000
Warrants expiration period				5 years
Warrants to purchase common stock, Issued				61,400,000		61,400,000		61,400,000
Common stock, shares issued				206,714,132		206,714,132		21,197,619
Registration right period				180 days
Escrow deposit		$ 598,500		$ 576,200		$ 578,900
Acquisition meaning				“Acquisition” means any acquisition by the Company (or any of its direct or indirect wholly-owned subsidiaries), in a single transaction or a series of transactions, whether by purchase, merger or otherwise, of all or substantially all of the assets of, or of 80% or more of the equity interests in, or a business line, unit or division of, any person.
Fixed conversion price of common stock									$ 1.35
Fair market value of embedded conversion feature, reclassed to equity						108,900
Changes in fair value					$ 18,029
Award vesting period				3 years
Number of additional Restricted Stock Awards Outstanding, Restricted stock awards granted				1,015,872
Unamortized value of unvested restricted share grant				$ 5,467		$ 3,500
Equity-based compensation				$ 102	140
Per share of unvested shares of common stock				$ 0.00001
Common stock, shares outstanding				206,714,132		206,714,132
Warrants to purchase common stock, outstanding				61,400,000		61,400,000
Exec Grants [Member]
Capital Stock Distribution [Line Items]
Share price				$ 2.25									$ 2.76
Restricted stock fair value				$ 5,000
Restricted stock price per share				$ 1.42
Chief Executive Officer [Member]
Capital Stock Distribution [Line Items]
Number of additional Restricted Stock Awards Outstanding, Restricted stock awards granted				507,936
Restricted stock award [Member]
Capital Stock Distribution [Line Items]
Amount of restricted stock grants	$ 400											$ 400
Share price	$ 1.20
Unvested shares				6,714,132		6,714,132					6,380,800
Number of Restricted Stock Awards Outstanding, Restricted stock awards granted	333,332			0		333,332
Restricted stock award [Member] | Exec Grants [Member]
Capital Stock Distribution [Line Items]
Amount of restricted stock grants				$ 4,000									$ 9,800
Restricted shares subject to repurchase [Member]
Capital Stock Distribution [Line Items]
Unvested shares				3,834,512		4,053,640					4,039,591
Number of Restricted Stock Awards Outstanding, Restricted stock awards granted						333,332
Minimum [Member]
Capital Stock Distribution [Line Items]
Preferred stock liquidation preference per share				$ 10.00
Convertible Series A Preferred Stock [Member]
Capital Stock Distribution [Line Items]
Preferred stock, par value				$ 0.00001		$ 0.00001
Preferred stock, shares issued				1,000,000		1,000,000									1,000,000
Purchase price of convertible preferred stock maximum limit							[1]								$ 11,100
Preferred stock liquidation preference				The Series A Preferred Stock has rights substantially similar to those associated with WMIH’s common stock, with the exception of a liquidation preference, conversion rights and customary anti-dilution protections. The Series A Preferred Stock has a liquidation preference equal to the greater of (i) $10.00 per one million shares of Series A Preferred Stock plus declared but unpaid dividends on such shares and (ii) the amount that the holder would be entitled to in a relevant transaction had the Series A Preferred Stock been converted to common stock of WMIH.
Convertible preferred stock conversion price				$ 1.10
Preferred deemed dividend				$ 9,500
Preferred stock, shares outstanding				1,000,000		1,000,000
Redeemable Convertible Series B Preferred Stock [Member]
Capital Stock Distribution [Line Items]
Preferred stock liquidation preference				If the Series B Preferred Stock is redeemed or determined likely to be redeemed, the Company would be required to record a charge to earnings of approximately $96.3 million to accrete the value of the Series B Preferred Stock to the $600.0 million redemption value. As of March 31, 2018, the Company has determined that recording for accretion to the Series B Preferred Stock’s redemption value is not required.
Amendment effective term				18 months
Amendment Effective Date				Jan. 05, 2018
Minimum percentage of preferred stock beneficially to be owned by KKR funds and its affiliates for acquisition consent				50.00%
Preferred stock, shares issued		600,000		600,000		600,000
Preferred stock dividend rate calculated on interest rate		3.00%
Preferred stock, redemption date				Oct. 05, 2019
Payments to acquire businesses				$ 450,000
Preferred stock, shares outstanding				600,000		600,000					600,000
Preferred stock, redemption amount				$ 600,000
Preferred stock, accretion to redemption value				$ 96,300
Number of trading periods				20 days
Conversion ceiling price of common stock				$ 2.25
Amendment Date				Dec. 08, 2017
Conversion floor price of common stock				$ 1.75						$ 1.75
Fixed conversion price of common stock									$ 1.35
Derivative liability - embedded conversion feature		$ 66,200
Derivative asset - embedded conversion feature					98,700
Fair market value of embedded conversion feature, reclassed to equity						$ 108,900
Changes in fair value					$ (18,000)
Preferred stock conversion price per share				1.35
Redeemable Convertible Series B Preferred Stock [Member] | Exec Grants [Member]
Capital Stock Distribution [Line Items]
Subject to minimum conversion price per share of restricted stock				1.75
Minimum grant conversion price per share of restricted stock				1.75
Preferred stock conversion price per share				1.35
Redeemable Convertible Series B Preferred Stock [Member] | Derivative Asset [Member]
Capital Stock Distribution [Line Items]
Conversion floor price of common stock										1.75
Redeemable Convertible Series B Preferred Stock [Member] | Derivative Liability [Member]
Capital Stock Distribution [Line Items]
Conversion ceiling price of common stock										$ 2.25
Redeemable Convertible Series B Preferred Stock [Member] | Maximum [Member]
Capital Stock Distribution [Line Items]
Conversion ceiling price of common stock				$ 2.25
Common Stock [Member]
Capital Stock Distribution [Line Items]
Issuance of common stock, Shares			200,000,000
Warrant One [Member]
Capital Stock Distribution [Line Items]
Warrants to purchase common stock															30,700,000
Warrants to purchase common stock, exercise price															$ 1.32
Warrant Two [Member]
Capital Stock Distribution [Line Items]
Warrants to purchase common stock															30,700,000
Warrants to purchase common stock, exercise price															$ 1.43
WMIH Common Stock [Member]
Capital Stock Distribution [Line Items]
Common stock, shares issued								21,197,619

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