Investments - Schedule of Other Long-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Long-Term Investment [Line Items]
Commercial mortgage loan participations	$ 907,390	$ 793,925
Commercial mortgage loan participations
Long-Term Investment [Line Items]
Commercial mortgage loan participations	140,069	141,843
Other
Long-Term Investment [Line Items]
Commercial mortgage loan participations	19,102	11,819
Partnership Interest - Fair Value Option \| Investment funds
Long-Term Investment [Line Items]
Commercial mortgage loan participations	$ 748,219	$ 640,263

Amount of long-term investments classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_OtherLongTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant