CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Class A	Class B Convertible	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning Balance at Dec. 31, 2013	$ 310,326	$ 15	$ 2	$ 494,086	$ (475,184)	$ (831)	$ 292,238
Beginning Balance (in shares) at Dec. 31, 2013		15,478	2,227		(6,405)
Net income	5,035	$ 0	$ 0	0	$ 0	0	5,035
Other comprehensive loss	(3,532)	0	0	0	0	(3,532)	0
Translation gain reclassified to other income	0
Conversion of class B to class A common stock	0	$ 0	$ 0	0	$ 0	0	0
Conversion of class B to class A common stock (in shares)		172	(172)		0
Issuance of class A common stock under stock option plans	$ 856	$ 1	$ 0	855	$ 0	0	0
Issuance of class A common stock under stock option plans (in shares)	9	10	0		0
Share-based compensation expense	$ 11,786	$ 0	$ 0	11,786	$ 0	0	0
Ending Balance at Dec. 31, 2014	324,471	$ 16	$ 2	506,727	$ (475,184)	(4,363)	297,273
Ending Balance (in shares) at Dec. 31, 2014		15,660	2,055		(6,405)
Net income	105,931	$ 0	$ 0	0	$ 0	0	105,931
Other comprehensive loss	(2,765)	0	0	0	0	(2,765)	0
Translation gain reclassified to other income	(280)	0	0	0	0	(280)	0
Conversion of class B to class A common stock	0	$ 0	$ 0	0	$ 0	0	0
Conversion of class B to class A common stock (in shares)		20	(20)		0
Issuance of class A common stock under stock option plans	$ 9,529	$ 0	$ 0	9,529	$ 0	0	0
Issuance of class A common stock under stock option plans (in shares)	91	91	0		0
Tax effect of stock option exercises	$ 1,096	$ 0	$ 0	1,096	$ 0	0	0
Share-based compensation expense	17,299	0	0	17,299	0	0	0
Ending Balance at Dec. 31, 2015	455,281	$ 16	$ 2	534,651	$ (475,184)	(7,408)	403,204
Ending Balance (in shares) at Dec. 31, 2015		15,771	2,035		(6,405)
Net income	90,908	$ 0	$ 0	0	$ 0	0	90,908
Other comprehensive loss	(3,335)	0	0	0	0	(3,335)	0
Translation gain reclassified to other income	0
Issuance of class A common stock under stock option plans	$ 1,663	$ 0	$ 0	1,663	$ 0	0	0
Issuance of class A common stock under stock option plans (in shares)	112	34	0		0
Tax effect of stock option exercises	$ 1,244	$ 0	$ 0	1,244	$ 0	0	0
Share-based compensation expense	11,817	0	0	11,817	0	0	0
Payment of taxes relating to net exercise of employee stock options	(3,739)	0	0	(3,739)	0	0	0
Write-off of deferred tax assets relating to vested employee stock options that are no longer exercisable	(1,662)	0	0	(1,662)	0	0	0
Ending Balance at Dec. 31, 2016	$ 552,177	$ 16	$ 2	$ 543,974	$ (475,184)	$ (10,743)	$ 494,112
Ending Balance (in shares) at Dec. 31, 2016		15,805	2,035		(6,405)