Summary of significant accounting policies (Details 5) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended							12 Months Ended
	May 03, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Concourse Communications Detroit, LLC	Dec. 31, 2012 Concourse Communications Detroit, LLC	Dec. 31, 2011 Concourse Communications Detroit, LLC	Dec. 31, 2009 Concourse Communications Detroit, LLC	Dec. 31, 2013 Chicago Concourse Development Group, LLC	Dec. 31, 2012 Chicago Concourse Development Group, LLC	Dec. 31, 2011 Chicago Concourse Development Group, LLC	Dec. 31, 2013 BHPL
Non-controlling interests
Initial term of Detroit Operating Agreement					7 years
Optional extension period of Detroit Operating Agreement					4 years
Non-controlling owners capital account amount		$ 865	$ 823					$ 0
Percentage of net profits less capital expenditures of the preceding year allocated to non-controlling interest holders									30.00%
Distributions to non-controlling interest holders		$ 608	$ 678	$ 547	$ 48	$ 121	$ 85		$ 560	$ 557	$ 462	$ 0
Convertible preferred stock
Preferred stock issued (in shares)		0	0
Preferred stock outstanding (in shares)		0	0
Warrants exercisable into convertible preferred stock
Preferred stock warrants outstanding (in shares)	25,196
Issuance of common stock upon exercise and conversion of preferred stock warrants (in shares)	20,172