Share Capital and Capital In Excess of Par Value (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Changes in share capital and capital in excess of par value
Balance at the beginning of the period			$ 782,882
Balance at the beginning of the period (in shares)			99
Purchase and retirement of common shares and other			$ (27,550)	$ (8,024)
Purchase and retirement of common shares and other (in shares)			(747)	(230)
Balance at the end of the period	$ 803,567	$ 783,323	$ 803,567	$ 783,323
Balance at the end of the period (in shares)	102	99	102	99
Stock dividends (as a percent)	3.00%	3.00%	3.00%	3.00%
Treasury Stock
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ (1,992)	$ (1,992)	$ (1,992)	$ (1,992)
Balance at the beginning of the period (in shares)	102	99	99	96
Issuance of 3% stock dividend (in shares)			3	3
Balance at the end of the period	$ (1,992)	$ (1,992)	$ (1,992)	$ (1,992)
Balance at the end of the period (in shares)	102	99	102	99
Capital in Excess of Par Value
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 753,839	$ 746,026	$ 719,606	$ 709,880
Issuance of 3% stock dividend			50,648	41,068
Purchase and retirement of common shares and other	(10,891)	(2,942)	(27,306)	(7,864)
Balance at the end of the period	742,948	743,084	742,948	743,084
Class B Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 20,453	$ 19,877	$ 19,866	$ 19,300
Balance at the beginning of the period (in shares)	29,452	28,623	28,607	27,793
Issuance of 3% stock dividend			$ 596	$ 579
Issuance of 3% stock dividend (in shares)			858	833
Conversion of Class B common shares to common shares			$ (9)	$ (3)
Conversion of Class B common shares to common shares (in shares)			(13)	(4)
Purchase and retirement of common shares and other				$ 1
Purchase and retirement of common shares and other (in shares)		(1)
Balance at the end of the period	$ 20,453	$ 19,877	$ 20,453	$ 19,877
Balance at the end of the period (in shares)	29,452	28,622	29,452	28,622
Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 28,118	$ 28,041	$ 27,584	$ 27,322
Balance at the beginning of the period (in shares)	40,490	40,379	39,721	39,344
Issuance of 3% stock dividend			$ 823	$ 817
Issuance of 3% stock dividend (in shares)			1,185	1,176
Conversion of Class B common shares to common shares			$ 9	$ 3
Conversion of Class B common shares to common shares (in shares)			13	4
Purchase and retirement of common shares and other	$ (221)	$ (59)	$ (519)	$ (160)
Purchase and retirement of common shares and other (in shares)	(318)	(85)	(747)	(230)
Balance at the end of the period	$ 27,897	$ 27,982	$ 27,897	$ 27,982
Balance at the end of the period (in shares)	40,172	40,294	40,172	40,294