Share Capital and Capital In Excess of Par Value (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 768,797
Balance at the beginning of the period (in shares)	96
Purchase and retirement of common shares	$ (1,152)	$ (7,423)
Purchase and retirement of common shares (in shares)	(33)	(234)
Balance at the end of the period	$ 769,506	$ 758,586
Balance at the end of the period (in shares)	99	96
Stock dividends (as a percent)	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)
Balance at the beginning of the period (in shares)	96	93
Issuance of 3% stock dividend (in shares)	3	3
Balance at the end of the period	$ (1,992)	$ (1,992)
Balance at the end of the period (in shares)	99	96
Capital in Excess of Par Value
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 709,880	$ 706,930
Issuance of 3% stock dividend	41,068	32,495
Purchase and retirement of common shares	(1,129)	(7,260)
Balance at the end of the period	749,819	732,165
Class B Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 19,300	$ 18,758
Balance at the beginning of the period (in shares)	27,793	27,012
Issuance of 3% stock dividend	$ 579	$ 562
Issuance of 3% stock dividend (in shares)	833	809
Balance at the end of the period	$ 19,879	$ 19,320
Balance at the end of the period (in shares)	28,626	27,821
Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 27,322	$ 27,134
Balance at the beginning of the period (in shares)	39,344	39,073
Issuance of 3% stock dividend	$ 817	$ 808
Issuance of 3% stock dividend (in shares)	1,176	1,163
Purchase and retirement of common shares	$ (23)	$ (163)
Purchase and retirement of common shares (in shares)	(33)	(234)
Balance at the end of the period	$ 28,116	$ 27,779
Balance at the end of the period (in shares)	40,487	40,002