Share Capital and Capital In Excess of Par Value (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 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			$ (16,548)	$ (5,023)
Purchase and retirement of common shares and other (in shares)			(429)	(145)
Balance at the end of the period	$ 785,074	$ 769,015	$ 785,074	$ 769,015
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	$ 768,676	$ 749,819	$ 719,606	$ 709,880
Issuance of 3% stock dividend			50,648	41,068
Purchase and retirement of common shares and other	(14,837)	(3,793)	(16,415)	(4,922)
Balance at the end of the period	753,839	746,026	753,839	746,026
Class B Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 20,460	$ 19,879	$ 19,866	$ 19,300
Balance at the beginning of the period (in shares)	29,463	28,626	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	$ (7)	$ (3)	$ (9)	$ (3)
Conversion of Class B common shares to common shares (in shares)	(11)	(4)	(13)	(4)
Purchase and retirement of common shares and other		$ 1		$ 1
Purchase and retirement of common shares and other (in shares)		1		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	28,623	29,452	28,623
Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 28,383	$ 28,116	$ 27,584	$ 27,322
Balance at the beginning of the period (in shares)	40,871	40,487	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	$ 7	$ 3	$ 9	$ 3
Conversion of Class B common shares to common shares (in shares)	11	4	13	4
Purchase and retirement of common shares and other	$ (272)	$ (78)	$ (298)	$ (101)
Purchase and retirement of common shares and other (in shares)	(392)	(112)	(429)	(145)
Balance at the end of the period	$ 28,118	$ 28,041	$ 28,118	$ 28,041
Balance at the end of the period (in shares)	40,490	40,379	40,490	40,379