Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Income from continuing operations	$ 96,298	$ 109,844	$ 137,810	$ 112,171					$ 456,123	$ 423,223	$ 381,519
Denominator for basic earnings per share—Weighted-average shares outstanding									306,897	304,722	302,343
Effect of dilutive securities:
RSUs									689	667	791
Stock options									2,198	2,107	2,905
Restricted stock									0	0	6
Denominator for diluted earnings per share—Adjusted weighted-average shares outstanding									309,784	307,496	306,045
Basic earnings per share from continuing operations	$ 0.31	$ 0.36	$ 0.45	$ 0.37	$ 0.31	$ 0.33	$ 0.39	$ 0.35	$ 1.49	$ 1.39	$ 1.26
Diluted earnings per share from continuing operations	$ 0.31	$ 0.35	$ 0.45	$ 0.36	$ 0.31	$ 0.33	$ 0.39	$ 0.35	$ 1.47	$ 1.38	$ 1.25