Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Common stock [Member]	Additional paid-in capital ("APIC") [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Non-controlling interest ("NCI") [Member]	Contingently Redeemable Performance Share Units [Member]	Total
Balance at Dec. 31, 2017	$ 138,582	$ 41,005	$ 602,609	$ (42,514)	$ 5,069	$ 9,014	$ 744,751
Balance, shares at Dec. 31, 2017	107,269,783
Net income			121,479		27		121,506
Other comprehensive loss				(13,763)	(29)
Other comprehensive income (loss)							(13,792)
Comprehensive income			121,479	(13,763)	(2)		107,714
Stock option exercises	$ 37,308	(8,784)					28,524
Stock option exercises, shares	1,235,154
Issuance of common stock related to vesting of share units	$ 5,890	(1,662)	(326)			(7,803)	3,902
Issuance of common stock related to vesting of share units, shares	177,093
Stock option compensation expense		8,252					8,252
Modification of PSUs		12,365	958			(6,622)	13,323
Equity-classified share unit expense		5,384				5,872	5,384
Equity-classified share units dividend equivalents		325	(678)			353	(353)
Change in value of contingently redeemable equity-classified PSUs			(109)			109	(109)
Cash dividends paid			(75,678)				(75,678)
Balance at Dec. 31, 2018	$ 181,780	56,885	648,255	(56,277)	5,067	923	835,710
Balance, shares at Dec. 31, 2018	108,682,030
Net income			149,039		101		149,140
Other comprehensive loss				(2,822)	(14)
Other comprehensive income (loss)							(2,836)
Comprehensive income			149,039	(2,822)	87		146,304
Stock option exercises	$ 49,117	(8,023)					41,094
Stock option exercises, shares	1,672,022
Issuance of common stock related to vesting of share units	$ 5,886	(10,064)	1			(1,083)	(4,177)
Issuance of common stock related to vesting of share units, shares	207,403
Stock option compensation expense		4,697					4,697
Equity-classified share unit expense		7,933				114	7,933
Equity-classified share units dividend equivalents		682	(709)			$ 46	(27)
Cash dividends paid			(82,535)				(82,535)
Shares repurchased	$ (42,012)						(42,012)
Shares repurchased, shares	(1,223,674)
Balance at Dec. 31, 2019	$ 194,771	52,110	714,051	(59,099)	5,154		906,987
Balance, shares at Dec. 31, 2019	109,337,781
Net income			170,095		263		170,358
Other comprehensive loss				24,804	57
Other comprehensive income (loss)							24,861
Comprehensive income			170,095	24,804	320		195,219
Stock option exercises	$ 55,669	(11,541)					44,128
Stock option exercises, shares	1,563,941
Issuance of common stock related to vesting of share units	$ 3,181	(9,900)					(6,719)
Issuance of common stock related to vesting of share units, shares	187,825
Issuance of common stock related to business combination		1,459					1,459
Issuance of common stock related to business combination, shares	312,193
Share based continuing employment costs		802					802
Stock option compensation expense		5,853					5,853
Equity-classified share unit expense		9,897					9,897
Equity-classified share units dividend equivalents		491	(491)
Cash dividends paid			(91,737)		(320)		(92,057)
Shares repurchased	$ (53,170)						(53,170)
Shares repurchased, shares	(1,525,312)
Balance at Dec. 31, 2020	$ 200,451	$ 49,171	$ 791,918	$ (34,295)	$ 5,154		$ 1,012,399
Balance, shares at Dec. 31, 2020	109,876,428