Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Outstanding Ordinary Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Beginning Balance, Amount at Jan. 31, 2014	$ 156,361	$ 13	$ 110,285	$ 0	$ 46,063
Beginning Balance, Shares at Jan. 31, 2014		28,748,513
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Amount	$ 8,508	$ 1	8,507	0	0
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Shares		1,456,944
Exercise of stock options, Shares	1,456,944
Vesting of early exercised stock options	$ 59	$ 0	59	0	0
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		484,296
Employee stock purchase plan, Amount	2,735	$ 0	2,735	0	0
Employee stock purchase plan, Shares		147,776
Stock-based compensation expense related to stock awards granted to employees and consultants	15,692	$ 0	15,692	0	0
Excess income tax benefit associated with stock-based compensation	3,286	0	3,286	0	0
Net unrealized losses on investments - net of taxes	(1)	0	0	(1)	0
Net income	50,571	0	0	0	50,571
Ending Balance, Amount at Jan. 31, 2015	237,211	$ 14	140,564	(1)	96,634
Ending Balance, Shares at Jan. 31, 2015		30,837,529
Exercise of stock options, Amount	$ 5,176	$ 1	5,175	0	0
Exercise of stock options, Shares	567,888	567,888
Restricted stock awards granted, Amount	$ 0	$ 0	0	0	0
Restricted stock awards granted, Shares		84,239
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		764,517
Employee stock purchase plan, Amount	3,100	$ 0	3,100	0	0
Employee stock purchase plan, Shares		79,186
Stock-based compensation expense related to stock awards granted to employees and consultants	31,094	$ 0	31,094	0	0
Excess income tax benefit associated with stock-based compensation	(3,627)	0	(3,627)	0	0
Net unrealized losses on investments - net of taxes	(6)	0	0	(6)	0
Net income	76,508	0	0	0	76,508
Ending Balance, Amount at Jan. 31, 2016	$ 349,456	$ 15	176,306	(7)	173,142
Ending Balance, Shares at Jan. 31, 2016	32,333,359	32,333,359
Cumulative effect of change in accounting principle	$ 11,688	$ 0	227	0	11,461
Exercise of stock options, Amount	$ 3,230	$ 0	3,230	0	0
Exercise of stock options, Shares	235,923	235,923
Restricted stock awards granted, Amount	$ 0	$ 0	0	0	0
Restricted stock awards granted, Shares		184,155
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		894,710
Employee stock purchase plan, Amount	4,034	$ 0	4,034	0	0
Employee stock purchase plan, Shares		125,974
Stock repurchase, Amount	$ (20,183)	$ 0	(20,183)	0	0
Stock repurchase, Shares	(405,089)	(405,089)
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 48,832	$ 0	48,832	0	0
Excess income tax benefit associated with stock-based compensation	(170)	0	(170)	0	0
Net unrealized losses on investments - net of taxes	(63)	0	0	(63)	0
Net income	57,810	0	0	0	57,810
Ending Balance, Amount at Jan. 31, 2017	$ 454,634	$ 15	$ 212,276	$ (70)	$ 242,413
Ending Balance, Shares at Jan. 31, 2017	33,369,032	33,369,032