Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Components of Earnings Per Share, Basic and Diluted [Line Items]
Distributed earnings	$ 15,455	$ 12,902	$ 30,851	$ 25,770
Undistributed earnings	21,154	17,046	38,086	32,857
Net income	36,609	29,948	68,937	58,627
Class A common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 24,730	$ 20,141	$ 46,537	$ 39,407
Basic weighted average common shares outstanding	27,434	27,082	27,376	27,037
Basic earnings per share	$ 0.90	$ 0.74	$ 1.70	$ 1.46
Diluted net income available to common stockholders	$ 24,830	$ 20,220	$ 46,741	$ 39,576
Effect of potential exercise of stock options	345	327	373	358
Diluted weighted average common shares outstanding	27,779	27,409	27,749	27,395
Diluted earnings per share	$ 0.89	$ 0.74	$ 1.68	$ 1.44
Class B common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 11,879	$ 9,807	$ 22,400	$ 19,220
Basic weighted average common shares outstanding	13,177	13,187	13,177	13,187
Basic earnings per share	$ 0.90	$ 0.74	$ 1.70	$ 1.46
Diluted net income available to common stockholders	$ 11,779	$ 9,728	$ 22,196	$ 19,051
Diluted weighted average common shares outstanding	13,177	13,187	13,177	13,187
Diluted earnings per share	$ 0.89	$ 0.74	$ 1.68	$ 1.44