Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Mar. 28, 2018	Mar. 14, 2018	Feb. 09, 2018	Nov. 14, 2017
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount		$ 227,500
Shares repurchased, number of shares received initially (in shares)	10,718,319	10,886,546
Fair value of common stock repurchased	$ 386,322	$ 397,572
Common Stock, Shares, Outstanding	276,210,910	279,222,277
Common Stock, Shares Authorized	560,000,000	560,000,000
Common Stock, Par or Stated Value Per Share	$ 0.10	$ 0.10	$ 0.10
Third Accelerated Share Repurchase Agreement [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount						$ 75,000
Shares repurchased, number of shares received initially (in shares)					168,227	1,290,486
Fair value of common stock repurchased					$ 11,200	$ 63,800
Treasury Stock, Shares, Acquired	1,458,713
Repurchase Agreements [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount		$ 100,000
2 for 1 Stock Split [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding			276,000,000	138,000,000
Common Stock, Shares Authorized			560,000,000	280,000,000