Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, shares in Millions						12 Months Ended
	Jan. 12, 2018	Dec. 14, 2017	Apr. 15, 2015	Feb. 26, 2015	Dec. 09, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 25, 2016
Common stock dividends paid	$ 59,400,000					$ 237,600,000	$ 216,100,000	$ 200,800,000
Dividends paid per common share (in dollars per share)		$ 0.63	$ 0.63
Dividends declared per common share						$ 2.52	$ 2.36	$ 2.20
Stock repurchase program, authorized amount									$ 200,000,000
Repurchases of common stock under stock repurchase program						0
Common stock repurchase authorization amount available						$ 193,000,000
Annual Dividend [Member]
Dividends declared per common share				$ 2.52	$ 2.20