Supplemental Information about Changes to Accumulated Other Comprehensive Income - Summary of Reclassifications (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ 26,097	$ (1,329)
Net investment income	(228,991)	(226,673)
Other operating expense	78,582	72,793
Total before tax	(202,921)	(228,101)
Tax	37,381	42,707
Total after-tax	(165,540)	(185,345)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	25,729	(256)
Reclassification out of Accumulated Other Comprehensive Income \| Unrealized Gains (Losses) on Available for Sale Assets
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	26,920	(3,670)
Net investment income	1,492	1,226
Total before tax	28,412	(2,444)
Tax	(5,967)	513
Total after-tax	22,445	(1,931)
Reclassification out of Accumulated Other Comprehensive Income \| Pension Adjustments
Unrealized investment (gains) losses on available for sale assets:
Total before tax	4,157	2,120
Tax	(873)	(445)
Total after-tax	3,284	1,675
Reclassification out of Accumulated Other Comprehensive Income \| Amortization of prior service cost
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	158	158
Reclassification out of Accumulated Other Comprehensive Income \| Amortization of actuarial (gain) loss
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	$ 3,999	$ 1,962

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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