Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Share Capital	Share Capital Class A Stock	Contributed Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period at Dec. 31, 2017		$ 58,492		$ 36,546	$ 426,930	$ 1,582
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A non-voting common stock			$ 333
Repurchase of Class A non-voting common stock for cancellation			0
Net Income (Loss) Attributable to Parent	$ 15,560				15,560
Share-based expense				3,096
Vested employee share plan awards				(355)
Dividends paid					(2,913)
Currency translation adjustment	(979)					(979)
Cumulative Effect on Retained Earnings, Net of Tax					349
Balance at end of period at Jun. 30, 2018	538,641	58,825		39,287	$ 439,926	603
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends					$ 0.22
Balance at beginning of period at Mar. 31, 2018		58,529		37,996	$ 432,544	1,440
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A non-voting common stock			296
Repurchase of Class A non-voting common stock for cancellation			0
Net Income (Loss) Attributable to Parent	8,855				8,855
Share-based expense				1,587
Vested employee share plan awards				(296)
Dividends paid					(1,457)
Currency translation adjustment	(837)					(837)
Cumulative Effect on Retained Earnings, Net of Tax					(16)
Balance at end of period at Jun. 30, 2018	538,641	58,825		39,287	$ 439,926	603
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends					$ 0.11
Balance at beginning of period 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			1,162
Repurchase of Class A non-voting common stock for cancellation			(6,352)
Net Income (Loss) Attributable to Parent	23,569
Share-based expense				4,026
Vested employee share plan awards				(2,176)
Dividends paid					(2,865)
Currency translation adjustment	924					924
Cumulative Effect on Retained Earnings, Net of Tax					0
Balance at end of period at Jun. 30, 2019	563,610	48,202		43,626	$ 470,693	1,089
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends					$ 0.22
Balance at beginning of period at Mar. 31, 2019		52,519		41,489	$ 459,751	728
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A non-voting common stock			0
Repurchase of Class A non-voting common stock for cancellation			$ (4,317)
Net Income (Loss) Attributable to Parent	12,375
Share-based expense				2,137
Vested employee share plan awards				0
Dividends paid					(1,433)
Currency translation adjustment	361					361
Cumulative Effect on Retained Earnings, Net of Tax					0
Balance at end of period at Jun. 30, 2019	$ 563,610	$ 48,202		$ 43,626	$ 470,693	$ 1,089
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends					$ 0.11