Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Operating revenues	$ 288,433	$ 268,771	$ 857,857	$ 802,120
Operating expenses:
Cost of revenues	62,986	65,593	188,288	202,891
Selling and marketing	41,514	38,809	125,057	122,485
Research and development	18,750	15,548	56,244	59,544
General and administrative	21,859	19,960	65,768	62,417
Amortization of intangible assets	11,752	11,710	35,535	35,107
Depreciation and amortization of property, equipment and leasehold improvements	8,312	8,049	24,873	23,321
Total operating expenses	165,173	159,669	495,765	505,765
Operating income	123,260	109,102	362,092	296,355
Interest income	(799)	(285)	(2,005)	(674)
Interest expense	26,790	17,267	72,612	39,491
Other expense (income)	(253)	(6,922)	2,642	(6,580)
Other expense (income), net	25,738	10,060	73,249	32,237
Income from continuing operations before provision for income taxes	97,522	99,042	288,843	264,118
Provision for income taxes	32,241	34,644	96,238	94,079
Income from continuing operations	65,281	64,398	192,605	170,039
Income (loss) from discontinued operations, net of income taxes				(5,797)
Net income	$ 65,281	$ 64,398	$ 192,605	$ 164,242
Earnings per basic common share:
Earnings per basic common share from continuing operations	$ 0.69	$ 0.59	$ 1.99	$ 1.53
Earnings per basic common share from discontinued operations				(0.05)
Earnings per basic common share	0.69	0.59	1.99	1.48
Earnings per diluted common share:
Earnings per diluted common share from continuing operations	0.68	0.59	1.98	1.52
Earnings per diluted common share from discontinued operations				(0.05)
Earnings per diluted common share	$ 0.68	$ 0.59	$ 1.98	$ 1.47
Weighted average shares outstanding used in computing earnings per share
Basic	94,823	108,773	96,879	111,131
Diluted	95,473	109,440	97,445	111,951
Dividend declared per common share	$ 0.28	$ 0.22	$ 0.72	$ 0.58