Capital Stock - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Capital Unit [Line Items]
Treasury stock, shares (shares)		23,130,924		23,240,197
Treasury shares, at cost		$ 329,025,000		$ 305,159,000
Common stock, shares authorized (shares)		180,000,000
Common stock, par value (dollars per share)		$ 0		$ 0
Common stock, shares, outstanding (shares)		38,950,467		38,841,194
Cumulative Preferred Stock
Capital Unit [Line Items]
Preferred stock, shares authorized (shares)		100,000
Preferred stock, par value (dollars per share)		$ 50
Percentage of 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)		120	0
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)		175,000	33,465
Common stock, shares issued (shares)				62,081,391
Stock issued during period, new issues (shares)		0
Common stock, value, issued (up to)		$ 100,000,000.0
Treasury stock
Capital Unit [Line Items]
Reissued shares (shares)		66,893	320,718
Preferred Stock
Capital Unit [Line Items]
Preferred stock, par value (dollars per share)		$ 50,000		$ 50,000
Percentage of cumulative preferred stock (percent)	4.50%	4.50%
Treasury shares, at cost		$ 1,800,000