Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from continuing operations [Abstract]
As reported	$ 2,017,438	$ 2,006,275	$ 1,993,351	$ 1,813,372	$ 1,777,961	$ 1,707,763	$ 1,686,345	$ 1,622,273	$ 7,830,436	$ 6,794,342	$ 6,956,311
Pro forma									7,841,835	7,494,468
Earnings from continuing operations [Abstract]
As reported	$ 296,448	$ 178,912	$ 164,058	$ 172,247	$ 161,162	$ 130,084	$ 118,290	$ 99,356	811,665	508,892	$ 595,881
Pro forma									$ 812,490	$ 550,176
Basic earnings per share from continuing operations [Abstract]
As reported (in dollars per share)	$ 1.90	$ 1.15	$ 1.05	$ 1.11	$ 1.04	$ 0.84	$ 0.76	$ 0.64	$ 5.21	$ 3.28	$ 3.78
Pro forma (in dollars per share)									5.22	3.54
Diluted earnings per share from continuing operations [Abstract]
As reported (in dollars per share)	$ 1.88	$ 1.14	$ 1.04	$ 1.09	$ 1.03	$ 0.83	$ 0.76	$ 0.64	5.15	3.25	$ 3.74
Pro forma (in dollars per share)									$ 5.15	$ 3.51