Condensed Consolidated Statements Of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Allocated Share-based Compensation Expense	$ 3,439	$ 3,168	$ 6,248	$ 6,173
Revenues:
Total revenues	211,800	176,038	412,302	337,291
Cost of revenues (1)	35,591	29,494	69,878	57,681
Gross Profit	176,209	146,544	342,424	279,610
Operating expenses:
Sales and marketing (1)	48,617	40,421	96,729	78,011
Research, development and engineering (1)	9,213	8,969	18,201	17,415
General and administrative (1)	59,434	47,088	115,211	93,588
Operating Expenses	117,264	96,478	230,141	189,014
Income from operations	58,945	50,066	112,283	90,596
Interest expense (income), net	10,301	10,881	20,534	21,194
Other expense (income), net	(213)	88	(87)	(696)
Income (loss) before income taxes	48,857	39,097	91,836	70,098
Income Tax Expense (Benefit)	15,087	181	28,123	9,304
Net Income (Loss) Attributable to Parent	$ 33,770	$ 38,916	$ 63,713	$ 60,794
Net income per common share:
Basic	$ 0.69	$ 0.81	$ 1.31	$ 1.26
Diluted	$ 0.69	$ 0.80	$ 1.30	$ 1.25
Weighted average shares outstanding:
Basic	48,055,783	47,537,597	48,011,250	47,480,315
Diluted	48,265,298	47,853,574	48,251,698	47,737,006
Cash dividends paid per common share	$ 0.3350	$ 0.3000	$ 0.6600	$ 0.5925
Cost of Sales [Member]
Allocated Share-based Compensation Expense	$ 103	$ 91	$ 198	$ 174
Selling and Marketing Expense [Member]
Allocated Share-based Compensation Expense	434	603	965	1,187
Research and Development Expense [Member]
Allocated Share-based Compensation Expense	221	213	428	408
General and Administrative Expense [Member]
Allocated Share-based Compensation Expense	$ 2,681	$ 2,261	$ 4,657	$ 4,404