Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of Earnings Per Share, Basic and Diluted [Line Items]
Distributed earnings	$ 15,475	$ 12,915	$ 46,326	$ 38,685
Undistributed earnings	22,481	16,824	60,567	49,681
Net income	37,956	29,739	106,893	88,366
Class A common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 25,663	$ 20,014	$ 72,200	$ 59,421
Basic weighted average common shares outstanding	27,512	27,139	27,421	27,071
Basic earnings per share	$ 0.93	$ 0.74	$ 2.63	$ 2.19
Diluted net income available to common stockholders	$ 25,754	$ 20,080	$ 72,495	$ 59,656
Effect of potential exercise of stock options	301	274	349	330
Diluted weighted average common shares outstanding	27,813	27,413	27,770	27,401
Diluted earnings per share	$ 0.93	$ 0.73	$ 2.61	$ 2.18
Class B common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 12,293	$ 9,725	$ 34,693	$ 28,945
Basic weighted average common shares outstanding	13,177	13,187	13,177	13,187
Basic earnings per share	$ 0.93	$ 0.74	$ 2.63	$ 2.19
Diluted net income available to common stockholders	$ 12,202	$ 9,659	$ 34,398	$ 28,710
Diluted weighted average common shares outstanding	13,177	13,187	13,177	13,187
Diluted earnings per share	$ 0.93	$ 0.73	$ 2.61	$ 2.18