Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Class A [Member]	Share Capital	Share Capital Common Class A [Member]	Contributed Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Parent	Non-Controlling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent			$ 58,492		$ 36,546	$ 426,930	$ 1,582
Dividends		$ 0.44				$ 0.44
Balance at beginning of year at Dec. 31, 2017									$ 361
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A non-voting common stock	$ 724			$ 794
Repurchase of Class A non-voting common stock for cancellation				(5,894)
Share-based expense					6,061
Vested employee share plan awards					(831)
Net Income (Loss) Attributable to Parent	28,892					$ 28,892
Dividends paid ($0.44 per share for the years 2012, 2013 & 2014)						(5,833)
Adjustments to Additional Paid in Capital, Other						(314)
Currency translation adjustment	(1,417)						(1,417)
Less net income (loss) attributable to non-controlling interest, net of tax									(16)
Dividends paid to non-controlling interest	372								(345)
Balance at end of year at Dec. 31, 2018	$ 545,322								0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent			53,392		41,776	$ 449,989	165	$ 545,322
Non-controlling interest									0
Dividends	$ 0.46	0.46				$ 0.46
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)
Net Income (Loss) Attributable to Parent	52,953					$ 52,953
Dividends paid ($0.44 per share for the years 2012, 2013 & 2014)						(5,944)
Adjustments to Additional Paid in Capital, Other						0
Currency translation adjustment	1,596						1,596
Less net income (loss) attributable to non-controlling interest, net of tax									0
Dividends paid to non-controlling interest	0								0
Balance at end of year at Dec. 31, 2019									0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent	$ 592,722		46,557		47,406	$ 496,998	1,761	592,722
Non-controlling interest									0
Dividends	$ 1.48	$ 1.48				$ 1.48
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)
Net Income (Loss) Attributable to Parent	122,986					$ 122,986
Dividends paid ($0.44 per share for the years 2012, 2013 & 2014)						(18,578)
Adjustments to Additional Paid in Capital, Other						0
Currency translation adjustment	1,687						1,687
Less net income (loss) attributable to non-controlling interest, net of tax									0
Dividends paid to non-controlling interest	0								0
Stockholders' Equity Attributable to Parent	$ 685,668		$ 39,333		$ 41,481	$ 601,406	$ 3,448	$ 685,668
Non-controlling interest									$ 0