Treasury Stock - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Mar. 31, 2017	Feb. 28, 2017
Class of Stock [Line Items]
Number of shares of common stock authorized to repurchase	36,000,000	36,000,000		1,000,000
Treasury stock, value	$ 430,989,000	$ 430,989,000	$ 419,802,000
Treasury stock, shares	34,881,055	34,881,055	34,631,834
Average price per share of common stock		$ 44.88
Common stock, shares outstanding	18,824,953	18,824,953	18,937,233
Number of shares of common stock repurchased	0	249,245
Treasury stock, value, acquired, cost method		$ 11,200,000
Nineteen Ninety Six Share Repurchase Program [Member]
Class of Stock [Line Items]
Common stock equals to percentage of outstanding common stock		65.00%
Average price per share of common stock		$ 12.36