Consolidated Statements of Changes in Stockholders' Equity and Redeemable Noncontrolling Interests - USD ($) $ in Thousands	Total	Share Capital	Share Capital Class A Stock	Contributed Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Parent	Non-Controlling Interest
Balance at beginning of year at Dec. 31, 2018		$ 53,392		$ 41,776	$ 449,989	$ 165
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A non-voting common stock	$ 2,192		$ 1,565
Repurchase of Class A non-voting common stock for cancellation			(8,400)
Share-based expense				8,128
Vested employee share plan awards				(2,498)
Change in redemption value of redeemable noncontrolling interests				0				$ 0
Net income	52,953				52,953
Dividends paid					(5,944)
Currency translation adjustment	1,596					1,596
Contributions during the year								0
Net loss attributable to non-controlling interest								0
Balance at end of year at Dec. 31, 2019	592,722	46,557		47,406	496,998	1,761	$ 592,722	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions during the year	0
Change in redemption value of redeemable noncontrolling interests	$ 0
Dividends paid per share (in dollars per share)	$ 0.46
Balance at end of year	$ 0
Issuance of Class A non-voting common stock	12,167		7,824
Repurchase of Class A non-voting common stock for cancellation			(15,048)
Share-based expense				7,683
Vested employee share plan awards				(13,608)
Change in redemption value of redeemable noncontrolling interests				0				0
Net income	122,986				122,986
Dividends paid					(18,578)
Currency translation adjustment	1,687					1,687
Contributions during the year								0
Net loss attributable to non-controlling interest								0
Balance at end of year at Dec. 31, 2020	685,668	39,333		41,481	601,406	3,448	685,668	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions during the year	0
Change in redemption value of redeemable noncontrolling interests	$ 0
Dividends paid per share (in dollars per share)	$ 1.48
Balance at end of year	$ 0
Issuance of Class A non-voting common stock	7,361		4,846
Repurchase of Class A non-voting common stock for cancellation			$ (7,737)
Share-based expense				10,514
Vested employee share plan awards				(9,739)
Change in redemption value of redeemable noncontrolling interests				(653)				(9,866)
Net income	158,964				158,964
Dividends paid					(19,444)
Currency translation adjustment	777					777
Contributions during the year								11,946
Net loss attributable to non-controlling interest	8							(11)
Balance at end of year at Dec. 31, 2021	825,265	$ 36,442		$ 41,603	$ 740,926	$ 4,225	$ 823,196	$ 2,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Contributions during the year	117,246
Change in redemption value of redeemable noncontrolling interests	$ 10,519
Dividends paid per share (in dollars per share)	$ 1.54
Balance at end of year	$ 127,765