Shareholders' Equity - Additional Information (Detail) - USD ($)	Sep. 30, 2016	Jan. 06, 2016	Dec. 31, 2015	Nov. 11, 2015	Aug. 11, 2015	Jul. 20, 2015	Mar. 05, 2015
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount	$ 250,000,000				$ 50,000,000	$ 400,000,000
Shares repurchased, number of shares received initially (in shares)	7,793,579		7,430,370		3,059,629
Fair value of common stock repurchased	$ 250,025,000		$ 238,775,000
Third Accelerated Share Repurchase Program [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount		$ 375,000,000
Shares repurchased, aggregate repurchase amount				$ (75,000,000)
Shares repurchased, number of shares received initially (in shares)		363,209		1,985,981
Fair value of common stock repurchased				$ 63,750,000
Accelerated Share Repurchase Agreement [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased, number of shares received initially (in shares)	7,793,579
Second Accelerated Share Repurchase Agreement
Accelerated Share Repurchases [Line Items]
Shares repurchased, aggregate repurchase amount							$ 100,000,000
Shares repurchased, number of shares received initially (in shares)					391,637		2,667,992
Fair value of common stock repurchased							$ 85,000,000
Repurchase Agreements [Member]
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount	$ 100,000,000