Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income available to stockholders on equivalent shares (Diluted EPS:)
Allocated net income (numerator)			$ 1,249
Weighted shares (denominator)			2,542
Per-share amount (in dollars per share)			$ 491
Class A common stock
Income available to stockholders (Basic EPS:)
Allocated net income (numerator)	$ 78,382	$ 81,306	$ 151,346	$ 140,146
Weighted shares (denominator)	46,188,289	46,187,808	46,188,573	46,188,299
Per-share amount (in dollars per share)	$ 1.70	$ 1.76	$ 3.28	$ 3.03
Dilutive effect of stock-based awards
Allocated net income (numerator)	$ 0	$ 0	$ 0	$ 0
Weighted shares (denominator)	13,281	14,373	19,790	24,568
Assumed conversion of Class B shares
Allocated net income (numerator)	$ 647	$ 671	$ 1,249	$ 1,157
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)	$ 79,029	$ 81,977	$ 152,595	$ 141,303
Weighted shares (denominator)	52,302,370	52,302,981	52,309,163	52,313,667
Per-share amount (in dollars per share)	$ 1.51	$ 1.57	$ 2.92	$ 2.70
Class B common stock
Income available to stockholders (Basic EPS:)
Allocated net income (numerator)	$ 647	$ 671	$ 1,249	$ 1,157
Weighted shares (denominator)	2,542	2,542	2,542	2,542
Per-share amount (in dollars per share)	$ 255	$ 264	$ 491	$ 455
Income available to stockholders on equivalent shares (Diluted EPS:)
Allocated net income (numerator)	$ 647	$ 671		$ 1,157
Weighted shares (denominator)	2,542	2,542	2,542	2,542
Per-share amount (in dollars per share)	$ 255	$ 264	$ 491	$ 455