Contractual maturities of cash, cash equivalent and short-term investment (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents (1)	$ 16,184	$ 39,652
Short-term investments	100,647	88,024
Cash, cash equivalents and short-term investments	116,831	127,676
Maturity up to one year
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents (1)	16,184	39,652
Short-term investments	84,589	71,464
Cash, cash equivalents and short-term investments	100,773	111,116
maturity between 1 and 2 years
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents (1)	0	0
Short-term investments	16,058	16,560
Cash, cash equivalents and short-term investments	$ 16,058	$ 16,560