Consolidated Statements Of Income - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 1,207,295,000	$ 1,117,838,000	$ 874,255,000
Cost of Revenue	201,074,000	172,313,000	147,100,000
Gross profit	1,006,221,000	945,525,000	727,155,000
Operating expenses:
Sales and marketing	338,304,000	330,296,000	206,871,000
Research, development and engineering	48,370,000	46,004,000	38,046,000
General and administrative	375,267,000	323,517,000	239,672,000
Total operating expenses	761,941,000	699,817,000	484,589,000
Income from operations	244,280,000	245,708,000	242,566,000
Interest expense, net	61,987,000	67,777,000	41,370,000
Other expense (income), net	4,706,000	(22,035,000)	(10,243,000)
Income before income taxes and net loss in earnings of equity method investment	177,587,000	199,966,000	211,439,000
Income tax expense	44,760,000	60,541,000	59,000,000
Net Loss from Equity Method Investments	4,140,000	0	0
Net income	$ 128,687,000	$ 139,425,000	$ 152,439,000
Net income per common share:
Basic (in dollars per share)	$ 2.64	$ 2.89	$ 3.15
Earnings Per Share, Diluted	$ 2.59	$ 2.83	$ 3.13
Weighted average shares outstanding:
Basic (in shares)	47,950,746	47,586,242	47,668,357
Diluted (in shares)	48,927,791	48,669,027	47,963,226
Cash dividends paid per common share (in dollars per share)	$ 1.68	$ 1.52	$ 1.36
Share-based compensation expense	$ 28,093,000	$ 22,737,000	$ 13,650,000
Cost of revenues
Share-based compensation expense	510,000	500,000	436,000
Sales and marketing
Share-based compensation expense	1,798,000	1,723,000	1,782,000
Research, development and engineering
Share-based compensation expense	1,553,000	1,182,000	904,000
General and administrative
Share-based compensation expense	$ 24,232,000	$ 19,332,000	$ 10,528,000