CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Cost of Common Stock in Treasury	Cost of Common Stock in Treasury Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Accumulated Other Comprehensive Income (Loss), Net	Accumulated Other Comprehensive Income (Loss), Net Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Income (Loss), Net Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Total Shareholders' Equity	Total Shareholders' Equity Cumulative Effect, Period of Adoption, Adjustment [Member]	Total Shareholders' Equity Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Noncontrolling Interests	Noncontrolling Interests Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Balance at Dec. 31, 2017	$ 718,537	$ 0	$ 718,537	$ 436,538	$ 436,538	$ 339,959	$ 718	$ 340,677	$ (54,628)	$ (54,628)	$ (3,332)	$ (718)	$ (4,050)	$ 718,537	$ 0	$ 718,537	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity
Net income	82,414					82,414								82,414
Other comprehensive income (loss)	(6,626)										(6,626)			(6,626)
Issuance of 46,089, 51,533, and 47,977 common shares under stock based compensation awards for 2020, 2019 and 2018, respectively	1,980					841			1,139					1,980
Cost of 166,446, 325,787, and 201,013 shares of common stock acquired for treasury for 2020, 2019 and 2018, respectively	(9,271)								(9,271)					(9,271)
Common stock dividend ($1.13, $1.10, and $0.96 per share for 2020, 2019 and 2018, respectively)	(24,952)					(24,952)								(24,952)
Contributions from noncontrolling interests	1,508													0			1,508
Balance at Dec. 31, 2018	$ 763,590	(301)	763,289	436,538	436,538	398,980	(301)	398,679	(62,760)	(62,760)	(10,676)		(10,676)	762,082	(301)	761,781	1,508	1,508
Increase (Decrease) in Stockholders' Equity
Issuance of common shares per stock based compensation awards, shares	47,977
Common stock acquired for treasury, shares	201,013
Common stock dividend (in dollars per share)	$ 0.96
Net income	$ 92,015					91,960								91,960			55
Other comprehensive income (loss)	15,848										15,848			15,848
Issuance of 46,089, 51,533, and 47,977 common shares under stock based compensation awards for 2020, 2019 and 2018, respectively	2,005					862			1,143					2,005
Cost of 166,446, 325,787, and 201,013 shares of common stock acquired for treasury for 2020, 2019 and 2018, respectively	(15,085)								(15,085)					(15,085)
Common stock dividend ($1.13, $1.10, and $0.96 per share for 2020, 2019 and 2018, respectively)	(28,232)					(28,232)								(28,232)
Contributions from noncontrolling interests	18,934													0			18,934
Distributions to noncontrolling interests	(138)													0			(138)
Balance at Dec. 31, 2019	$ 848,636	$ (2,552)	$ 846,084	436,538	$ 436,538	463,269	$ (2,552)	$ 460,717	(76,702)	$ (76,702)	5,172		$ 5,172	828,277	$ (2,552)	$ 825,725	20,359	$ 20,359
Increase (Decrease) in Stockholders' Equity
Issuance of common shares per stock based compensation awards, shares	51,533
Common stock acquired for treasury, shares	325,787
Common stock dividend (in dollars per share)	$ 1.10
Net income	$ 81,461					81,437								81,437			24
Other comprehensive income (loss)	13,199										13,199			13,199
Issuance of 46,089, 51,533, and 47,977 common shares under stock based compensation awards for 2020, 2019 and 2018, respectively	1,839					962			877					1,839
Cost of 166,446, 325,787, and 201,013 shares of common stock acquired for treasury for 2020, 2019 and 2018, respectively	(6,415)								(6,415)					(6,415)
Common stock dividend ($1.13, $1.10, and $0.96 per share for 2020, 2019 and 2018, respectively)	(28,940)					(28,940)								(28,940)
Contributions from noncontrolling interests	24,098													0			24,098
Distributions to noncontrolling interests	(656)													0			(656)
Balance at Dec. 31, 2020	$ 930,670			$ 436,538		$ 514,176			$ (82,240)		$ 18,371			$ 886,845			$ 43,825
Increase (Decrease) in Stockholders' Equity
Issuance of common shares per stock based compensation awards, shares	46,089
Common stock acquired for treasury, shares	166,446
Common stock dividend (in dollars per share)	$ 1.13