Capital Stock - Narrative (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Capital Unit [Line Items]
Preferred stock, par value (dollars per share)	$ 50,000		$ 50,000
Cumulative preferred stock (percent)	4.50%		4.50%
Treasury stock, shares (shares)	22,891,759		23,013,489
Treasury shares, at cost	$ 331,039,000		$ 327,756,000
Common stock, shares authorized (shares)	180,000,000
Common stock, par value (dollars per share)	$ 0
Common stock, shares, outstanding (shares)	39,189,632		39,067,902
Cumulative Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares authorized (shares)	100,000
Preferred stock, par value (dollars per share)	$ 50
Cumulative preferred stock (percent)	4.50%
Preferred stock, callable price per share (dollars per share)	$ 52.50
Preferred stock, shares issued (shares)	71,340
Treasury stock, shares (shares)	52,998
Purchase of treasury shares (shares)	0	120
Second Cumulative Preferred Voting Stock
Capital Unit [Line Items]
Preferred stock, shares authorized (shares)	1,000,000
Preferred stock, par value (dollars per share)	$ 10
Preferred stock, shares issued (shares)	0
Common Stock
Capital Unit [Line Items]
Purchase of treasury shares (shares)	0	175,000
Common stock, shares issued (shares)			62,081,391
Stock issued during period, new issues (shares)	0	0
Common stock, value, issued (up to)	$ 100,000,000.0
Treasury stock
Capital Unit [Line Items]
Reissued shares (shares)	33,625	63,405
Preferred Stock
Capital Unit [Line Items]
Treasury shares, at cost	$ 1,800,000