Earnings Per Share (Schedule of Earnings Per Share, Basic and Diluted) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Components of Earnings Per Share, Basic and Diluted [Line Items]
Distributed earnings	$ 15,396	$ 12,868
Undistributed earnings	16,932	15,811
Net income	32,328	28,679
Class A common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 21,809	$ 19,266
Basic weighted average common shares outstanding	27,317	26,992
Basic earnings per share	$ 0.80	$ 0.71
Diluted net income available to common stockholders	$ 21,912	$ 19,353
Effect of potential exercise of stock options	401	375
Diluted weighted average common shares outstanding	27,718	27,367
Diluted earnings per share	$ 0.79	$ 0.71
Class B common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 10,519	$ 9,413
Basic weighted average common shares outstanding	13,177	13,187
Basic earnings per share	$ 0.80	$ 0.71
Diluted net income available to common stockholders	$ 10,416	$ 9,326
Diluted weighted average common shares outstanding	13,177	13,187
Diluted earnings per share	$ 0.79	$ 0.71