Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class A common stock
Income available to stockholders (Basic EPS:)
Allocated net income (numerator)	$ 89,484	$ 88,486	$ 240,830	$ 228,632
Weighted shares (denominator)	46,189,035	46,189,030	46,188,729	46,188,544
Per-share amount (in dollars per share)	$ 1.94	$ 1.92	$ 5.21	$ 4.95
Dilutive effect of stock-based awards
Allocated net income (numerator)	$ 0	$ 0	$ 0	$ 0
Weighted shares (denominator)	15,410	20,599	18,330	23,244
Assumed conversion of Class B shares
Allocated net income (numerator)	$ 739	$ 730	$ 1,988	$ 1,887
Weighted shares (denominator)	6,100,800	6,100,800	6,100,800	6,100,800
Income available to stockholders on equivalent shares (Diluted EPS:)
Allocated net income (numerator)	$ 90,223	$ 89,216	$ 242,818	$ 230,519
Weighted shares (denominator)	52,305,245	52,310,429	52,307,859	52,312,588
Per-share amount (in dollars per share)	$ 1.72	$ 1.71	$ 4.64	$ 4.41
Class B common stock
Income available to stockholders (Basic EPS:)
Allocated net income (numerator)	$ 739	$ 730	$ 1,988	$ 1,887
Weighted shares (denominator)	2,542	2,542	2,542	2,542
Per-share amount (in dollars per share)	$ 291	$ 287	$ 782	$ 742
Income available to stockholders on equivalent shares (Diluted EPS:)
Allocated net income (numerator)	$ 739	$ 730	$ 1,988	$ 1,887
Weighted shares (denominator)	2,542	2,542	2,542	2,542
Per-share amount (in dollars per share)	$ 291	$ 287	$ 782	$ 742