Acquisitions (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($) Acquisitions
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			$ 68,557	$ 25,568
Goodwill, Acquired During Period			46,472
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					$ 34,300
Number of Businesses Acquired | Acquisitions					2
Revenue [Abstract]
As reported	$ 1,798,094	$ 1,737,371	3,435,765	3,320,581
Pro forma	1,798,094	1,746,950	3,436,081	3,342,851
Net earnings [Abstract]
As reported	166,456	142,475	275,865	297,563
Pro forma	$ 168,158	$ 142,167	$ 279,714	$ 296,459
Basic earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	$ 1.10	$ 0.92	$ 1.80	$ 1.91
Pro forma (in dollars per share) | $ / shares	1.11	0.91	1.83	1.90
Diluted earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	1.08	0.90	1.77	1.89
Pro forma (in dollars per share) | $ / shares	$ 1.09	$ 0.90	$ 1.80	$ 1.88
Ettlinger Group [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition of 100 Percent, Voting Rights			100.00%
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 19,730		$ 19,730
Ettiingler [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			53,218
Goodwill, Acquired During Period			$ 36,070
Rosario [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition of 100 Percent, Voting Rights			100.00%
Payments to Acquire Businesses, Net of Cash Acquired			$ 15,339
Goodwill, Acquired During Period			10,402
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 4,149		$ 4,149
Caldera Graphics [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired				$ 32,680
Goodwill, Acquired During Period				24,649
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		$ 8,169		$ 8,169
Minimum [Member] | Ettiingler [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			8 years
Minimum [Member] | Rosario [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			10 years
Minimum [Member] | Caldera Graphics [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				7 years
Maximum [Member] | Ettiingler [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