Common stock (Options outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Change in Fair Value Of Warrant Liability Recorded in Other Income (Expense)	$ 0	$ (1,600,000)	$ (1,000,000)
Weighted-average grant-date fair value (in dollars per share)	$ 7.34	$ 10.19	$ 3.30
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, Beginning balance	3,187,559
Options granted	(675,460)
Options exercised	(420,492)
Options cancelled	(142,102)
Options expired	(13,221)
Number of Options, Outstanding, Ending balance	3,287,204	3,187,559
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 7.51
Options granted	$ 16.85
Options exercised	$ 3.94
Options cancelled	$ 12.17
Options expired	$ 22.47
Weighted Average Exercise Price, Outstanding, Ending balance	$ 9.62	$ 7.51
Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]
Aggregate Intrinsic Value, Options Outstanding	24,880,000	56,362,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]
Options vested and expected to vest (Number of options)	3,238,937,000
Options vested and expected to vest (Wtd avg exercise price)	$ 9,510
Options vested and expected to vest (Wtd avg remaining contractual term)	6 years 4 months 28 days
Options vested and expected to vest (Aggregate intrinsic value)	24,824,000
Options vested and exercisable (Number of options)	1,996,061,000
Options vested and exercisable (Wtd avg exercise price)	$ 5,820
Options vested and exercisable (Wtd avg remaining contractual term)	5 years 0 months 18 days
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized net compensation cost related to options	$ 8,200,000
Weighted average period (in years)	2 years 6 months 4 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Wtd Avg Remaining Contractual Term, Options Outstanding	6 years 5 months 12 days	6 years 9 months 22 days
Wtd Avg Remaining Contractual Term, Options Outstanding	6 years 5 months 12 days	6 years 9 months 22 days