Investments - Schedule of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2014	Jan. 31, 2014
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	$ 977,545	$ 537,136
Unrealized Gains on Marketable Securities	4,314	2,560
Unrealized Losses on Marketable Securities	(907)	(314)
Fair Value of Marketable Securities	980,952	539,382
Corporate notes and obligations
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	596,671	340,706
Unrealized Gains on Marketable Securities	2,186	1,314
Unrealized Losses on Marketable Securities	(439)	(170)
Fair Value of Marketable Securities	598,418	341,850
U.S. treasury securities
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	56,563	16,016
Unrealized Gains on Marketable Securities	94	28
Unrealized Losses on Marketable Securities	(28)	0
Fair Value of Marketable Securities	56,629	16,044
Mortgage backed obligations
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	46,629	24,888
Unrealized Gains on Marketable Securities	192	281
Unrealized Losses on Marketable Securities	(302)	(93)
Fair Value of Marketable Securities	46,519	25,076
Asset backed securities
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	125,599	38,213
Unrealized Gains on Marketable Securities	88	39
Unrealized Losses on Marketable Securities	(43)	(35)
Fair Value of Marketable Securities	125,644	38,217
Municipal securities
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	38,976	2,000
Unrealized Gains on Marketable Securities	38	1
Unrealized Losses on Marketable Securities	(79)	(3)
Fair Value of Marketable Securities	38,935	1,998
Foreign government obligations
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	20,031	24,305
Unrealized Gains on Marketable Securities	309	171
Unrealized Losses on Marketable Securities	0	(2)
Fair Value of Marketable Securities	20,340	24,474
U.S. agency obligations
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	17,987	14,726
Unrealized Gains on Marketable Securities	12	9
Unrealized Losses on Marketable Securities	(16)	(10)
Fair Value of Marketable Securities	17,983	14,725
Covered bonds
Investment Holdings [Line Items]
Amortized Cost on Marketable Securities	75,089	76,282
Unrealized Gains on Marketable Securities	1,395	717
Unrealized Losses on Marketable Securities	0	(1)
Fair Value of Marketable Securities	$ 76,484	$ 76,998