Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2012

Summary of significant accounting policies

Schedule of depreciation and amortization computed using the straight-line method over the estimated useful lives of assets

Computer equipment	2 to 5 years
Software	2 to 5 years
Office equipment	3 to 5 years
Leasehold improvements	The shorter of the estimated useful life or the remaining term of the agreements, generally ranging from 3 to 15 years

Schedule of weighted average assumptions used to calculate the grant date fair values of employee stock option grants

	December 31,
	2012			2011			2010
Expected term (years)		5.9			6.4			6.1
Expected volatility		48.9	%		49.8	%		67.6	%
Risk-free rate		0.9	%		2.4	%		2.5	%
Dividend yield		0	%		0	%		0	%

Summary of the entity's revenue by primary revenue source

	Year Ended December 31,
	2012		2011		2010
Revenue:
Retail subscription	$	32,716	$	29,033	$	23,561
Retail single-use		13,429		16,054		17,460
Wholesale		49,495		43,707		35,134
Advertising and other		6,866		5,764		4,265
Total revenue	$	102,506	$	94,558	$	80,420