Cash, Cash Equivalents, and Investments - Summary of Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 364,523
Gross Unrealized Gains	1,280
Gross Unrealized Losses	(411)
Fair Value	365,392
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	171,405
Corporate bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	60,871
Gross Unrealized Gains	111
Gross Unrealized Losses	(20)
Fair Value	60,962
Corporate bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	109,693
Gross Unrealized Gains	796
Gross Unrealized Losses	(46)
Fair Value	110,443
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	65,319
Asset-backed securities [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,984
Gross Unrealized Gains	20
Gross Unrealized Losses	(22)
Fair Value	22,982
Asset-backed securities [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,581
Gross Unrealized Gains	25
Gross Unrealized Losses	(269)
Fair Value	42,337
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	29,571
Municipal bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,917
Gross Unrealized Gains	35
Gross Unrealized Losses
Fair Value	12,952
Municipal bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,477
Gross Unrealized Gains	142
Gross Unrealized Losses
Fair Value	16,619
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	39,278
Agency bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,502
Gross Unrealized Gains
Gross Unrealized Losses	(9)
Fair Value	11,493
Agency bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,720
Gross Unrealized Gains	89
Gross Unrealized Losses	(24)
Fair Value	27,785
Treasury bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	33,727
Treasury bills [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,602
Gross Unrealized Gains	2
Gross Unrealized Losses
Fair Value	5,604
Treasury bills [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,117
Gross Unrealized Gains	7
Gross Unrealized Losses	(1)
Fair Value	28,123
Covered bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	11,271
Covered bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,676
Gross Unrealized Gains	1
Gross Unrealized Losses	(17)
Fair Value	4,660
Covered bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,591
Gross Unrealized Gains	20
Gross Unrealized Losses
Fair Value	6,611
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,998
Commercial paper [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,998
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	2,998
Sovereign bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	11,823
Sovereign bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000
Gross Unrealized Gains
Gross Unrealized Losses	(3)
Fair Value	1,997
Sovereign bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,794
Gross Unrealized Gains	32
Gross Unrealized Losses
Fair Value	$ 9,826