Common stock (Details)	6 Months Ended				6 Months Ended						6 Months Ended						6 Months Ended		0 Months Ended
	Jun. 30, 2014		Jun. 30, 2014 Common Stock	Dec. 31, 2013 Common Stock	Jun. 30, 2014 Common Class A		Jun. 30, 2014 Common Class B		Jun. 30, 2014 Common Class C	Dec. 31, 2013 Common Class C	Jun. 30, 2014 Common Class D		Jun. 30, 2014 Common Class E	Dec. 31, 2013 Common Class E	Jun. 30, 2014 Common Class F	Dec. 31, 2013 Common Class F	Jun. 30, 2014 Common Class G		Jan. 13, 2014 Healthcare of Ontario Pension Plan Trust Fund Common Class A	Jan. 13, 2014 Class A Common Stock Converted from Class D and Class G Common Stock Healthcare of Ontario Pension Plan Trust Fund Common Class A	Jan. 13, 2014 Class A Common Stock Converted from Class B Common Stock Healthcare of Ontario Pension Plan Trust Fund Common Class A
Common stock rollforward
Shares outstanding at January 1, 2014			1,424,722	1,422,160	70,117		357,882		209,882	209,882	279,999		504,276	504,276	1	1	3
Stock transfers	0	[1]			293,023	[1]	(13,023)	[1]			(279,999)	[1]					(1)	[1]			13,023	[1]
Restricted stock issuances	4,613				4,613
Restricted stock repurchased	(1,390)				(1,390)
Restricted stock forfeitures	(661)				(661)
Shares outstanding at June 30, 2014			1,424,722	1,422,160	365,702		344,859		209,882	209,882	0		504,276	504,276	1	1	2
Company shares bought and sold by Company stockholders																			15,078	280,000

[1] In this transaction, Healthcare of Ontario Pension Plan Trust Fund (“HOOPP”) purchased 280,000 shares of Class A common stock converted from Class D and Class G common stock held by CHK Energy Holdings, Inc. (“CHK Energy Holdings”) effective January 13, 2014. An additional 15,078 shares of Class A common stock was purchased by HOOPP from various other stockholders of which 13,023 shares were converted from Class B common stock.