Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, shares in Millions			3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 13, 2018	May 15, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Feb. 25, 2016
Common stock dividends paid					$ 118,900,000	$ 118,800,000
Dividends declared per common share			$ 0.79	$ 0.63	$ 1.42	$ 1.26
Dividends declared date					May 15, 2018
Dividends paid per common share (in dollars per share)		$ 0.79
Stock repurchase program, authorized amount								$ 200,000,000
Repurchases of common stock under stock repurchase program			0		0
Common stock repurchase authorization amount available			$ 193,000,000		$ 193,000,000
Annual Dividend [Member]
Dividends declared per common share		$ 3.16					$ 2.52
Subsequent Event
Common stock dividends paid	$ 74,500,000