Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
reinsurance contract obligation [Line Items]
Minimum commitment under noncancelable purchase obligations	$ 697.5
unrecorded unconditional purchase obligations reinsurance [Member] \| Lower Limit
reinsurance contract obligation [Line Items]
Reinsurance Contract Terms	1 year
Other Commitment	$ 81.5
unrecorded unconditional purchase obligations reinsurance [Member] \| Upper Limit
reinsurance contract obligation [Line Items]
Reinsurance Contract Terms	3 years

Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25336-109308

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant