Condensed Consolidated Statements Of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Revenues	$ 344,141	$ 292,724	$ 966,466	$ 861,236
Cost of Revenue	61,716	49,217	172,995	145,112
Gross profit	282,425	243,507	793,471	716,124
Operating expenses:
Sales and marketing (1)	98,486	80,708	273,812	250,190
Research, development and engineering (1)	13,770	11,950	38,692	35,412
General and administrative (1)	110,810	93,792	314,132	272,926
Total operating expenses	223,066	186,450	626,636	558,528
Income from operations	59,359	57,057	166,835	157,596
Interest expense, net	17,271	15,175	50,625	46,428
Other expense, net	864	1,239	2,702	6,150
Income before income taxes and net loss (income) in earnings of equity method investment	41,224	40,643	113,508	105,018
Income tax expense	6,998	9,310	17,851	23,365
Net loss (income) in earnings of equity method investment	3,481	610	(126)	3,581
Net income	$ 30,745	$ 30,723	$ 95,783	$ 78,072
Net income per common share:
Basic	$ 0.63	$ 0.63	$ 1.98	$ 1.61
Diluted EPS impact	$ 0.62	$ 0.61	$ 1.93	$ 1.57
Weighted average shares outstanding:
Basic	47,673,211	48,009,953	47,654,327	47,945,264
Diluted	49,064,272	49,279,217	48,892,523	49,068,653
Share-based Payment Arrangement, Expense	$ 6,446	$ 7,906	$ 18,394	$ 21,393
Cost of Sales [Member]
Share-based Payment Arrangement, Expense	127	128	390	378
Selling and Marketing Expense [Member]
Share-based Payment Arrangement, Expense	419	548	1,212	1,380
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense	373	399	1,092	1,187
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expense	$ 5,527	$ 6,831	$ 15,700	$ 18,448