Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Class A [Member] Common Stock [Member]	Common Class A [Member] Additional Paid-in Capital [Member]	Common Class A [Member] Treasury Stock [Member]	Common Class A [Member] Retained Earnings [Member]	Common Class A [Member] AOCI Attributable to Parent [Member]	Common Class A [Member]	Common Class B [Member] Common Stock [Member]	Common Class B [Member] Additional Paid-in Capital [Member]	Common Class B [Member] Treasury Stock [Member]	Common Class B [Member] Retained Earnings [Member]	Common Class B [Member] AOCI Attributable to Parent [Member]	Common Class B [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2018	43,065						12,435
Balance at Dec. 31, 2018													$ 458	$ 370,025	$ (245,842)	$ 942,287	$ 0	$ 1,066,928
Stock options exercised and stock awards (in shares)	586						0
Stock options exercised and stock awards													4	7,585	0	0	0	7,589
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan													0	19,005	0	0	0	19,005
Vesting of restricted share awards (in shares)	0						339
Vesting of restricted share awards													2	(2,834)	0	0	0	(2,832)
Issuance of common stock under employee stock purchase plan (in shares)	175						0
Issuance of common stock under employee stock purchase plan													1	3,486	0	0	0	3,487
Common stock repurchases (in shares)	(1,896)						(414)
Common stock repurchases													0	0	(58,287)	0	0	(58,287)
Cash dividends declared	$ 0	$ 0	$ 0	$ (14,037)	$ 0	$ (14,037)	$ 0	$ 0	$ 0	$ (4,280)	$ 0	$ (4,280)
Other comprehensive income (loss)													0	0	0	0	337	337
Net income													0	0	0	141,583	0	141,583
Balance (in shares) at Dec. 31, 2019	41,930						12,360
Balance at Dec. 31, 2019													465	397,267	(304,129)	1,065,553	337	1,159,493
Stock options exercised and stock awards (in shares)	1,247						0
Stock options exercised and stock awards													10	19,582	0	0	0	19,592
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan													0	19,356	0	0	0	19,356
Vesting of restricted share awards													2	(2,459)	0	0	0	(2,457)
Issuance of common stock under employee stock purchase plan (in shares)	177						0
Issuance of common stock under employee stock purchase plan													2	3,900	0	0	0	3,902
Common stock repurchases (in shares)	(843)						(225)
Common stock repurchases													0	0	(24,807)	0	0	(24,807)
Cash dividends declared	$ 0	0	0	(17,062)	0	(17,062)	$ 0	0	0	(5,399)	0	(5,399)
Other comprehensive income (loss)													0	0	0	0	532	532
Net income													0	0	0	114,887	0	114,887
Cancellation of treasury stock (in shares)	(7)						(4)
Cancellation of treasury stock													72	0	326,057	(326,129)	0
Balance (in shares) at Dec. 31, 2020	42,504						12,470
Balance at Dec. 31, 2020													551	437,646	(2,879)	831,850	869	$ 1,268,037
Stock options exercised and stock awards (in shares)	784						0											768,668
Stock options exercised and stock awards													8	14,157	0	0	0	$ 14,165
Stock-based compensation related to stock options, restricted shares and employee stock purchase plan													0	22,246	0	0	0	22,246
Vesting of restricted share awards (in shares)	0						347
Vesting of restricted share awards													3	(7,447)	0	0	0	(7,444)
Issuance of common stock under employee stock purchase plan (in shares)	149						0
Issuance of common stock under employee stock purchase plan													1	4,148	0	0	0	4,149
Common stock repurchases (in shares)	(329)						(418)
Common stock repurchases													0	0	(34,054)	0	0	(34,054)
Cash dividends declared	$ 0	$ 0	$ 0	$ (31,816)	$ 0	$ (31,816)	$ 0	$ 0	$ 0	$ (9,867)	$ 0	$ (9,867)
Other comprehensive income (loss)													0	0	0	0	(82)	(82)
Net income													0	0	0	241,415	0	241,415
Balance (in shares) at Dec. 31, 2021	43,108						12,399
Balance at Dec. 31, 2021													$ 563	$ 470,750	$ (36,933)	$ 1,031,582	$ 787	$ 1,466,749