Investments - Schedule of Other Long-Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Long-Term Investment [Line Items]
Commercial mortgage loan participations	$ 793,925	$ 546,981
Commercial mortgage participations
Long-Term Investment [Line Items]
Commercial mortgage loan participations	141,843	160,602
Other
Long-Term Investment [Line Items]
Commercial mortgage loan participations	11,819	1,341
Partnership Interest - Fair Value Option | Investment funds
Long-Term Investment [Line Items]
Commercial mortgage loan participations	$ 640,263	$ 385,038