Shareholders' Equity - Additional Information (Detail) - USD ($)		18 Months Ended
	Sep. 02, 2014	Jun. 30, 2015	Aug. 11, 2015	Mar. 05, 2015	Dec. 31, 2014	Jul. 21, 2014	Jun. 30, 2014
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount							$ 25,000,000
Total number of shares repurchased (in shares)		5,444,389
Shares repurchased, number of shares received initially (in shares)		5,053,000	3,059,629		2,385,000
Fair value of common stock repurchased		$ 160,025,000			$ 75,025,000
Maximum
Accelerated Share Repurchases [Line Items]
Shares repurchased, authorized amount						$ 200,000,000
Accelerated Share Repurchase Agreement
Accelerated Share Repurchases [Line Items]
Shares repurchased, aggregate repurchase amount	$ 50,000,000
Total number of shares repurchased (in shares)	1,539,760
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