Income Taxes - Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards	$ 31,532	$ 31,532
Deferred tax liabilities:
Insurance intangible	307,290		$ 336,728
Variable interest entities	42,232		46,343
Investments	91,231		38,656
Unearned premiums and credit fees	64,807		68,682
Undistributed Earnings of Foreign Subsidiaries	74,459		30,699
Other	4,173		4,276
Deferred Tax Liabilities, Gross, Noncurrent	584,192	525,384
Deferred tax assets:
Net operating loss and capital carryforward	1,490,682		1,409,565
Loss reserves	269,597		224,553
Other	8,878		11,967
Sub total deferred tax assets	1,805,656	1,682,376
Valuation allowance	1,223,394		1,158,712
Total deferred tax assets	582,262	523,664
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	4,967		$ 4,759
Deferred Tax Liabilities, Net	$ 1,930	$ 1,720