Financial Assets & Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	$ 357,339	$ 260,056
Contingent consideration	(2,385)	(3,749)
Net asset (liability)	354,954	256,307
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	286,000	205,000
Contingent consideration	0	0
Net asset (liability)	286,000	205,000
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	71,339	55,056
Contingent consideration	0	0
Net asset (liability)	71,339	55,056
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Contingent consideration	(2,385)	(3,749)
Net asset (liability)	(2,385)	(3,749)
Money market funds
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	286,000	205,000
Money market funds | Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	286,000	205,000
Money market funds | Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Money market funds | Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Bank time deposits
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	71,339	55,056
Bank time deposits | Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Bank time deposits | Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	71,339	55,056
Bank time deposits | Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets & Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	$ 0	$ 0