Fair Value Measurements (Details 1) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jan. 31, 2014
Total [Member]
Assets:
Assets measured at fair value	$ 370,583
Liabilities:
Liabilities measured at fair value	2,234
Level 1 [Member]
Assets:
Assets measured at fair value	243,454
Liabilities:
Liabilities measured at fair value	0
Level 2 [Member]
Assets:
Assets measured at fair value	125,479
Liabilities:
Liabilities measured at fair value	2,234
Level 3 [Member]
Assets:
Assets measured at fair value	1,650
Liabilities:
Liabilities measured at fair value	0
Cash and Cash Equivalents [Member] | Total [Member]
Assets:
Assets measured at fair value	256,364
Cash and Cash Equivalents [Member] | Level 1 [Member]
Assets:
Assets measured at fair value	241,365
Cash and Cash Equivalents [Member] | Level 2 [Member]
Assets:
Assets measured at fair value	14,999
Cash and Cash Equivalents [Member] | Level 3 [Member]
Assets:
Assets measured at fair value	0
Short-term Investments [Member] | Total [Member]
Assets:
Assets measured at fair value	94,993
Short-term Investments [Member] | Level 1 [Member]
Assets:
Assets measured at fair value	0
Short-term Investments [Member] | Level 2 [Member]
Assets:
Assets measured at fair value	94,993
Short-term Investments [Member] | Level 3 [Member]
Assets:
Assets measured at fair value	0
Prepaid Expenses and Other Current Assets [Member] | Total [Member]
Assets:
Assets measured at fair value	501
Prepaid Expenses and Other Current Assets [Member] | Level 1 [Member]
Assets:
Assets measured at fair value	52
Prepaid Expenses and Other Current Assets [Member] | Level 2 [Member]
Assets:
Assets measured at fair value	449
Prepaid Expenses and Other Current Assets [Member] | Level 3 [Member]
Assets:
Assets measured at fair value	0
Marketable Securities Noncurrent [Member] | Total [Member]
Assets:
Assets measured at fair value	15,038
Marketable Securities Noncurrent [Member] | Level 1 [Member]
Assets:
Assets measured at fair value	0
Marketable Securities Noncurrent [Member] | Level 2 [Member]
Assets:
Assets measured at fair value	15,038
Marketable Securities Noncurrent [Member] | Level 3 [Member]
Assets:
Assets measured at fair value	0
Other Noncurrent Assets [Member] | Total [Member]
Assets:
Assets measured at fair value	3,687
Other Noncurrent Assets [Member] | Level 1 [Member]
Assets:
Assets measured at fair value	2,037
Other Noncurrent Assets [Member] | Level 2 [Member]
Assets:
Assets measured at fair value	0
Other Noncurrent Assets [Member] | Level 3 [Member]
Assets:
Assets measured at fair value	1,650
Accrued Liabilities [Member] | Total [Member]
Liabilities:
Liabilities measured at fair value	2,234
Accrued Liabilities [Member] | Level 1 [Member]
Liabilities:
Liabilities measured at fair value	0
Accrued Liabilities [Member] | Level 2 [Member]
Liabilities:
Liabilities measured at fair value	2,234
Accrued Liabilities [Member] | Level 3 [Member]
Liabilities:
Liabilities measured at fair value	$ 0