Treasury Stock and Subsequent Event - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended
	Oct. 30, 2015	Sep. 30, 2015	Sep. 30, 2015	Mar. 31, 2015	Aug. 31, 2013
Class of Stock [Line Items]
Treasury stock, value		$ 379,053,000	$ 379,053,000	$ 360,278,000
Treasury stock, shares		33,552,190	33,552,190	32,992,488
Average price		$ 32.37	$ 33.55
Common stock, shares outstanding		19,787,279	19,787,279	20,250,669
Number of shares repurchased		299,620	559,702
Treasury Stock, Value, Acquired, Cost Method		$ 9,700,000	$ 18,800,000
Nineteen Ninety Six Share Repurchase Program [Member]
Class of Stock [Line Items]
Common stock equals to percentage of outstanding common stock			63.00%
Average price			$ 11.30
Minimum [Member]
Class of Stock [Line Items]
Number of shares authorized to repurchase					2,000,000
Maximum [Member]
Class of Stock [Line Items]
Number of shares authorized to repurchase					34,000,000
Subsequent Event [Member]
Class of Stock [Line Items]
Average price	$ 33.07
Number of shares repurchased	99,403
Treasury Stock, Value, Acquired, Cost Method	$ 3,287,000