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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of Earnings Per Share, Basic and Diluted [Line Items]
Distributed earnings	$ 12,915	$ 10,823	$ 38,685	$ 32,360
Undistributed earnings	16,824	17,114	49,681	40,909
Net income	29,739	27,937	88,366	73,269
Class A common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 20,014	$ 18,729	$ 59,421	$ 49,048
Basic weighted average common shares outstanding	27,139	26,822	27,071	26,706
Basic earnings per share	$ 0.74	$ 0.70	$ 2.19	$ 1.84
Diluted net income available to common stockholders	$ 20,080	$ 18,798	$ 59,656	$ 49,203
Effect of potential exercise of stock options	274	306	330	257
Diluted weighted average common shares outstanding	27,413	27,128	27,401	26,963
Diluted earnings per share	$ 0.73	$ 0.69	$ 2.18	$ 1.82
Class B common stock
Components of Earnings Per Share, Basic and Diluted [Line Items]
Basic net income available to common stockholders	$ 9,725	$ 9,208	$ 28,945	$ 24,221
Basic weighted average common shares outstanding	13,187	13,188	13,187	13,188
Basic earnings per share	$ 0.74	$ 0.70	$ 2.19	$ 1.84
Diluted net income available to common stockholders	$ 9,659	$ 9,139	$ 28,710	$ 24,066
Diluted weighted average common shares outstanding	13,187	13,188	13,187	13,188
Diluted earnings per share	$ 0.73	$ 0.69	$ 2.18	$ 1.82