Acquisitions (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Dec. 31, 2016 USD ($) Acquisitions
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			$ 25,568	$ 501,828
Goodwill, Acquired During Period			$ 24,649	314,633
Finite-lived Intangible Assets Acquired				208,838
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					$ 1,562,000
Business Combination, Assets and Liabilities Arising from Contingencies, Amount Recognized, Net					$ 1,554,000
Document Fiscal Year Focus			2017
Number of Businesses Acquired | Acquisitions					6
Revenue [Abstract]
As reported	$ 2,006,275	$ 1,707,763	$ 5,812,998	5,016,381
Pro forma	2,006,275	1,897,781	5,816,109	5,596,612
Net earnings [Abstract]
As reported	178,912	130,084	515,217	347,730
Pro forma	$ 178,912	$ 136,681	$ 515,668	$ 371,900
Basic earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	$ 1.15	$ 0.84	$ 3.31	$ 2.24
Pro forma (in dollars per share) | $ / shares	1.15	0.88	3.31	2.40
Diluted earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	1.14	0.83	3.27	2.22
Pro forma (in dollars per share) | $ / shares	$ 1.14	$ 0.87	$ 3.27	$ 2.38
Caldera Graphics [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition of 100 Percent, Voting Rights			100.00%
Payments to Acquire Businesses, Net of Cash Acquired			$ 32,680
Goodwill, Acquired During Period			24,649
Finite-lived Intangible Assets Acquired			$ 8,169
Minimum [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				8 years
Minimum [Member] | Caldera Graphics [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			7 years
Maximum [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				15 years
Maximum [Member] | Caldera Graphics [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			15 years