Equity - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2021	May 27, 2021	May 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 14, 2019	Dec. 31, 2018	Sep. 30, 2015
Class of Stock [Line Items]
Quarterly dividend on all classes of common stock (in dollars per share)					$ 0.88	$ 0.80	$ 0.70
Share expiration period					10 years
SARs exercise price (in dollars per share)					$ 88.68		$ 82.76
Excess tax benefits related to stock-based awards					$ 292,000	$ (440,000)	$ 449,000
Decrease in additional paid-in capital					(1,300,000)	(600,000)	(1,800,000)
Intrinsic value of outstanding, exercisable and vested or excepted to vest restricted stock	$ 20,400,000				20,400,000	8,500,000
Intrinsic value of shares exercised					900,000	$ 700,000	$ 1,900,000
Unrecognized compensation cost	3,300,000				$ 3,300,000
Weighted-average period of recognition					1 year 9 months 18 days
Weighted-average grant date fair value (in dollars per share)					$ 65.48	$ 45.91	$ 58.27
Compensation expense					$ 4,300,000	$ 4,100,000	$ 2,300,000
Granted (in dollars per share)					$ 88.92	$ 66.02	$ 80.51
Capital required for capital adequacy	713,800,000				$ 713,800,000	$ 680,900,000
Capital	1,200,000,000				1,200,000,000	1,000,000,000
Excess capital	$ 486,800,000				$ 486,800,000	325,500,000
Outstanding, SARs (in shares)	130,409				130,409
Stock Appreciation Rights (SARs) [Member]
Class of Stock [Line Items]
Tax benefit from exercise of SARs					$ 900,000	$ 500,000	$ 1,000,000
Outstanding, SARs (in shares)	130,409				130,409	116,417	98,836			124,960
Stock option
Class of Stock [Line Items]
Outstanding, SARs (in shares)	0				0
Minimum
Class of Stock [Line Items]
SARs exercise price (in dollars per share)						$ 72.26
Minimum | Restricted Stock
Class of Stock [Line Items]
Vesting period					1 year	1 year	1 year
Maximum
Class of Stock [Line Items]
SARs exercise price (in dollars per share)						$ 75.16
Maximum | Restricted Stock
Class of Stock [Line Items]
Vesting period					3 years	3 years	3 years
Series G
Class of Stock [Line Items]
Number of shares issued (in shares)			5,000,000
Preferred stock, dividend rate		4.875%	4.875%
Preferred stock, par value (in dollars per share)	$ 25		$ 25.00		$ 25	$ 25
Payments of stock issuance costs		$ 3,661,677	$ 3,700,000
Class C non-voting common stock
Class of Stock [Line Items]
Stock authorized for repurchase									$ 10,000,000		$ 25,000,000
Shares repurchased (in shares)	673,000			4,000	0
Shares repurchased	$ 19,800,000			$ 200,000
Remaining authorized amount for repurchase								$ 9,800,000