Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2013	23,329	2,562
Balance at Dec. 31, 2013	$ 268,255	$ 319	$ 22,598	$ (1,538)	$ 245,088	$ 534,722
Net income					138,720	138,720
Gain on cash flow hedges, net of tax expense of $175, $399 and $380				612		612
Issuance of stock in connection with employee stock plans (in shares)	118
Issuance of stock in connection with employee stock plans	$ 4,590					4,590
Issuance of restricted stock to employees (in shares)	288
Repurchase of Class A common stock (in shares)	(333)
Repurchase of Class A common stock	$ (22,968)					(22,968)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	$ 6,445		7,177			13,622
Issuance of stock in connection with acquisitions (in shares)	269
Issuance of stock in connection with acquisitions	$ 19,736					19,736
Dividends paid					(15,929)	(15,929)
Balance (in shares) at Dec. 31, 2014	23,671	2,562
Balance at Dec. 31, 2014	$ 276,058	$ 319	29,775	(926)	367,879	673,105
Net income					182,999	182,999
Gain on cash flow hedges, net of tax expense of $175, $399 and $380				649		649
Issuance of stock in connection with employee stock plans (in shares)	74
Issuance of stock in connection with employee stock plans	$ 6,065					6,065
Issuance of restricted stock to employees (in shares)	217
Repurchase of Class A common stock (in shares)	(306)
Repurchase of Class A common stock	$ (31,548)					(31,548)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	$ 7,832		9,047			16,879
Dividends paid					(19,985)	(19,985)
Balance (in shares) at Dec. 31, 2015	23,676	2,542
Balance at Dec. 31, 2015	$ 258,410	$ 316	38,822	(277)	530,893	828,164
Class B common stock converted to Class A common stock (in shares)	20
Class B common stock converted to Class A common stock	$ 3	$ (3)
Class B common stock converted to Class A common stock (in shares)		(20)
Net income					197,058	197,058
Gain on cash flow hedges, net of tax expense of $175, $399 and $380				$ 277		277
Issuance of stock in connection with employee stock plans (in shares)	93
Issuance of stock in connection with employee stock plans	$ 6,932					6,932
Issuance of restricted stock to employees (in shares)	241
Repurchase of Class A common stock (in shares)	(1,408)
Repurchase of Class A common stock	$ (112,939)					(112,939)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	$ 13,012		2,403			15,415
Dividends paid					(24,131)	(24,131)
Balance (in shares) at Dec. 31, 2016	23,382	1,762
Balance at Dec. 31, 2016	$ 165,512	$ 219	$ 41,225		$ 703,820	$ 910,776
Class B common stock converted to Class A common stock (in shares)	780
Class B common stock converted to Class A common stock	$ 97	$ (97)
Class B common stock converted to Class A common stock (in shares)		(780)