CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014
Income Statement [Abstract]
Service revenue	$ 222,506	$ 204,751	$ 633,666	$ 588,099
Product revenue	126,959	122,816	375,786	380,015
Total revenue	349,465	327,567	1,009,452	968,114
Costs and expenses:
Cost of services provided	145,165	144,053	425,614	415,976
Cost of products sold	66,225	65,246	193,320	199,423
Selling, general and administrative	76,225	64,476	218,953	196,999
Amortization of intangible assets	6,410	7,620	17,385	18,813
Operating income	55,440	46,172	154,180	136,903
Other income (expense):
Interest income	177	376	758	803
Interest expense	(3,851)	(2,997)	(11,251)	(9,171)
Other income (expense), net	1,390	331	1,749	8,874
Income from continuing operations, before income taxes	53,156	43,882	145,436	137,409
Provision for income taxes	15,255	11,582	26,662	36,021
Income from continuing operations, net of income taxes	37,901	32,300	118,774	101,388
Income (loss) from discontinued operations, net of income taxes	(34)	52	(48)	(862)
Net income	37,867	32,352	118,726	100,526
Less: Net income attributable to noncontrolling interests	(488)	(316)	(1,297)	(994)
Net income attributable to common shareholders	$ 37,379	$ 32,036	$ 117,429	$ 99,532
Basic:
Continuing operations attributable to common shareholders (in dollars per share)	$ 0.81	$ 0.70	$ 2.52	$ 2.15
Discontinued operations (in dollars per share)	0.00	0.00	0.00	(0.02)
Net income attributable to common shareholders (in dollars per share)	0.81	0.70	2.52	2.13
Diluted:
Continuing operations attributable to common shareholders (in dollars per share)	0.79	0.68	2.47	2.11
Discontinued operations (in dollars per share)	0.00	0.00	0.00	(0.02)
Net income attributable to common shareholders (in dollars per share)	$ 0.79	$ 0.68	$ 2.47	$ 2.09