Equity and redeemable securities (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		0 Months Ended	6 Months Ended	12 Months Ended			0 Months Ended					0 Months Ended					0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Aug. 14, 2013 Subsequent Event [Member]	Jun. 30, 2013 Convertible Class C Preferred Stock [Member]	Dec. 31, 2012 Convertible Class C Preferred Stock [Member]	Jan. 26, 2012 Convertible Class C Preferred Stock [Member]	Dec. 31, 2011 Convertible Class C Preferred Stock [Member]	Aug. 14, 2013 Convertible Class C Preferred Stock [Member] Subsequent Event [Member]	Jun. 30, 2013 Redeemable Class B Senior Preferred Stock [Member]	Dec. 31, 2012 Redeemable Class B Senior Preferred Stock [Member]	Dec. 31, 2011 Redeemable Class B Senior Preferred Stock [Member]	Jun. 30, 2009 Redeemable Class B Senior Preferred Stock [Member]	Aug. 14, 2013 Redeemable Class B Senior Preferred Stock [Member] Subsequent Event [Member]	Jun. 30, 2013 Redeemable Class A Junior Preferred Stock [Member]	Dec. 31, 2012 Redeemable Class A Junior Preferred Stock [Member]	Dec. 31, 2011 Redeemable Class A Junior Preferred Stock [Member]	May 05, 2009 Redeemable Class A Junior Preferred Stock [Member]	Aug. 14, 2013 Redeemable Class A Junior Preferred Stock [Member] Subsequent Event [Member]	Jun. 30, 2013 Class A Common Stock [Member]	Dec. 31, 2012 Class A Common Stock [Member]	Jun. 30, 2012 Class A Common Stock [Member]	Jun. 30, 2013 Class B Common Stock [Member]	Dec. 31, 2012 Class B Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized					300,000,000																22,725,500	22,725,500		3,246,500	3,246,500
Common stock, par value					$ 0.01																$ 0.01	$ 0.01		$ 0.01	$ 0.01
Temporary equity, shares authorized						5,000	5,000	5,000			500,000	500,000		500,000		10,000	10,000		10,000
Temporary equity, par value						$ 0.01	$ 0.01	$ 0.01			$ 0.01	$ 0.01		$ 0.01		$ 0.01	$ 0.01		$ 0.01
Temporary equity, shares issued						5,000	5,000				75,000	75,000				10,000	10,000
Temporary equity, shares outstanding						5,000	5,000		0		37,467	36,388	48,760			5,100	5,100	5,100
Conversion of preferred stock (shares)					7,191,891					4,454,889					2,736,637					365
Temporary equity, liquidation preference per share														$ 1,000					$ 1.00
Temporary equity, dividend rate														8.00%
Temporary equity, dividends earned but not declared or paid											$ 483	$ 89
Temporary equity, common stock shares issued if converted						4,454,889
Temporary equity, conversion price						$ 1.122
Share price (dollars per share)					$ 14.00																		$ 2.25
Recognition of beneficial conversion feature	0	0	0	5,000		5,000	5,000
Deemed dividend						$ 5,000	$ 5,000
Deemed dividend, impact on earnings per share						$ (0.39)