Net Income Per Share - Computation of Basic and Diluted Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 80,773	$ 97,465	$ 174,138	$ 166,451
Shares used in net income per share computation:
Weighted average shares outstanding - basic (in shares)	164,248	161,977	163,924	162,070
Effect of potentially dilutive equivalent shares (in shares)	4,831	3,924	4,908	3,141
Weighted average shares outstanding - diluted (in shares)	169,079	165,901	168,832	165,211
Net income per share:
Net income per share - basic (in dollars per share)	$ 0.49	$ 0.60	$ 1.06	$ 1.03
Net income per share - diluted (in dollars per share)	$ 0.48	$ 0.59	$ 1.03	$ 1.01
Anti-dilutive equivalents shares excluded (in shares)	500	1,700	1,100	2,800