Cash, Cash Equivalents, and Investments - Effective Maturity Dates of Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	$ 123,648
1-2 Years	112,310
2-3 Years	112,159
3-4 Years	13,230
4-5 Years	4,045
Fair Value	365,392
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	60,962
1-2 Years	36,566
2-3 Years	64,948
3-4 Years	7,381
4-5 Years	1,548
Fair Value	171,405
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	22,982
1-2 Years	34,387
2-3 Years	7,950
3-4 Years
4-5 Years
Fair Value	65,319
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	11,493
1-2 Years	20,385
2-3 Years	6,477
3-4 Years
4-5 Years	923
Fair Value	39,278
Treasury bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	5,604
1-2 Years	4,503
2-3 Years	23,620
3-4 Years
4-5 Years
Fair Value	33,727
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	12,952
1-2 Years	11,181
2-3 Years	2,437
3-4 Years	1,427
4-5 Years	1,574
Fair Value	29,571
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	2,998
1-2 Years
2-3 Years
3-4 Years
4-5 Years
Fair Value	2,998
Sovereign bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	1,997
1-2 Years	1,522
2-3 Years	6,727
3-4 Years	1,577
4-5 Years
Fair Value	11,823
Covered bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 1 Year	4,660
1-2 Years	3,766
2-3 Years
3-4 Years	2,845
4-5 Years
Fair Value	$ 11,271