Acquisitions (Details) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($) Acquisitions
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 68,385	$ 0
Goodwill, Acquired During Period	$ 46,907
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			$ 43,142
Document Fiscal Year Focus	2018
Number of Businesses Acquired | Acquisitions			3
Revenue [Abstract]
As reported	$ 1,921,579	1,813,372
Pro forma	1,921,895	1,825,997
Net earnings [Abstract]
As reported	131,435	172,247
Pro forma	$ 133,406	$ 171,085
Basic earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	$ 0.85	$ 1.11
Pro forma (in dollars per share) | $ / shares	0.86	1.10
Diluted earnings per share [Abstract]
As reported (in dollars per share) | $ / shares	0.84	1.09
Pro forma (in dollars per share) | $ / shares	$ 0.85	$ 1.09
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	$ 20,084
Ettiingler [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	53,046
Goodwill, Acquired During Period	$ 36,505
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
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
Maximum [Member] | Ettiingler [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years