CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Current assets:
Cash equivalent investments	$ 795,365	$ 867,112
Accounts receivable, allowance for doubtful accounts	2,006	2,003
Assets, Noncurrent [Abstract]
Accumulated amortization	$ 355,563	$ 322,689
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized (in shares)	1,000	1,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	1,000,000	1,000,000
Common stock, shares issued (in shares)	431,932	430,385
Treasury stock, shares (in shares)	163,928	163,886