Business and Significant Accounting Policies - Additional Information (Detail) $ in Millions			3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 21, 2018 shares	Feb. 20, 2018 shares	Dec. 31, 2019 USD ($)	Dec. 31, 2020 property	Dec. 31, 2019 USD ($) segment foundation trust	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business And Significant Accounting Policies [Line Items]
Number of reportable segments | segment					2
Percentage of contractual participation					100.00%
Number of statutory trusts | trust					11
Number of charitable foundations | foundation					1
Stock dividend declared, percent						15.00%
Allowance for doubtful accounts			$ 7.3		$ 7.3	$ 4.0
Reinsurance recoverables, allowance for doubtful accounts			1.1		1.1	1.8
Estimated liability for return of premiums					5.4	6.9
Estimated amount of premiums receivables due					0.3	0.4
Impairment of goodwill			15.6		$ 15.6	0.0	$ 0.0
Weighted average useful life					5 years
Amortization expense					$ 1.7	3.3	5.9
Estimated amortization expense, year one			1.3		1.3
Estimated amortization expense, year two			1.3		1.3
Estimated amortization expense, year three			0.1		0.1
Accumulated depreciation for property and equipment			153.2		153.2	146.0
Net book value of property and equipment			140.4		140.4	154.8
Depreciation expense					24.4	24.5	$ 24.1
Foreign currency translation adjustment			$ 22.6		22.6	$ 22.4
Other Corporate Expenses [Member]
Business And Significant Accounting Policies [Line Items]
Loss on disposition of property plant equipment					$ 3.7
Forecast [Member]
Business And Significant Accounting Policies [Line Items]
Number of properties sold | property				4
Minimum [Member]
Business And Significant Accounting Policies [Line Items]
Useful life					3 years
Maximum [Member]
Business And Significant Accounting Policies [Line Items]
Useful life					39 years
Distribution Network [Member]
Business And Significant Accounting Policies [Line Items]
Weighted average useful life					5 years
Other [Member]
Business And Significant Accounting Policies [Line Items]
Weighted average useful life					5 years
Stock Dividend [Member]
Business And Significant Accounting Policies [Line Items]
Stock dividend declared, percent		15.00%
Additional stock issued as dividend (in shares) | shares	4,397,520	4,397,520