Stockholders' Equity - Summary of Cash Dividends Paid (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended			36 Months Ended
	Feb. 14, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Feb. 09, 2018
Equity [Abstract]
Total Cash Dividends Paid		$ 119.7	$ 121.6	$ 106.8	$ 348.1
Total Cash Dividends Paid Per Common Share (in usd per share)		$ 0.64	$ 0.61	$ 0.52
Subsequent Event [Line Items]
Dividends declared date		Feb. 14, 2018
Dividends per share on common stock		$ 0.64	$ 0.61	$ 0.52
Dividends declared payable date		Mar. 16, 2018
Dividends declared date of record		Mar. 02, 2018
Common stock, shares outstanding		168,595,521	193,482,383	196,013,299	193,482,383
Subsequent Event
Subsequent Event [Line Items]
Dividends per share on common stock	$ 0.16
Estimated dividend payment						$ 26.8
Common stock, shares outstanding						167,000,000