Income Taxes - Summary of Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected federal income tax expense (benefit)	$ 191,602	$ 188,304	$ 195,569
Low income housing investments	(12,115)	(11,913)	(11,605)
Share-based awards	(5,597)	(5,013)	(11,780)
Tax-exempt investment income	(6,977)	(5,830)	(3,192)
Other	518	(637)	1,405
Income tax expense (benefit)	$ 167,431	$ 164,911	$ 170,397
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected federal income tax expense (benefit)	21.00%	21.00%	21.00%
Low income housing investments	(1.30%)	(1.30%)	(1.20%)
Share-based awards	(0.60%)	(0.60%)	(1.30%)
Tax-exempt investment income	(0.80%)	(0.60%)	(0.30%)
Other	0.10%	(0.10%)	0.10%
Income tax expense (benefit)	18.40%	18.40%	18.30%