Condensed Consolidated Statements Of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Total revenues	$ 280,623	$ 254,669
Cost of revenues (1)	48,145	40,810
Gross profit	232,478	213,859
Operating expenses:
Sales and marketing (1)	86,311	77,477
Research, development and engineering (1)	12,210	11,752
General and administrative (1)	87,799	76,655
Total operating expenses	186,320	165,884
Income from operations	46,158	47,975
Interest (income) expense, net	15,751	12,410
Other expense, net	4,519	323
Income before income taxes	25,888	35,242
Income tax expense	7,017	9,422
Net income	$ 18,871	$ 25,820
Net income per common share:
Basic	$ 0.39	$ 0.54
Diluted	$ 0.38	$ 0.52
Weighted average shares outstanding:
Basic	47,873,007	47,463,231
Diluted	48,706,717	48,766,031
Cash dividends paid per common share	$ 0.4050	$ 0.3650
Allocated Share-based Compensation Expense	$ 6,420	$ 3,614
Cost of Sales [Member]
Allocated Share-based Compensation Expense	121	117
Selling and Marketing Expense [Member]
Allocated Share-based Compensation Expense	365	378
Research and Development Expense [Member]
Allocated Share-based Compensation Expense	432	238
General and Administrative Expense [Member]
Allocated Share-based Compensation Expense	$ 5,502	$ 2,881