Stockholders' equity Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2014

Stockholders' Equity Note [Abstract]

Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Performance-Based Units, Vested and Expected to Vest [Table Text Block]

The following is a summary of the changes in our common shares outstanding during the years ended December 31, 2014, 2013 and 2012:

	Common Stock
	Class A		Class B		Class C	Class D		Class E	Class F	Class G		Total
Shares issued at January 1, 2012	66,165		357,882		209,882	279,999		504,276	1	3		1,418,208
Restricted stock issuance	17,494		—		—	—		—	—	—		17,494
Restricted stock repurchased	(1,469	)	—		—	—		—	—	—		(1,469	)
Restricted stock forfeited	(14,199	)	—		—	—		—	—	—		(14,199	)
Shares issued at December 31, 2012	67,991		357,882		209,882	279,999		504,276	1	3		1,420,034
Restricted stock issuance	8,056		—		—	—		—	—	—		8,056
Restricted stock repurchased	(1,025	)	—		—	—		—	—	—		(1,025	)
Restricted stock forfeited	(4,905	)	—		—	—		—	—	—		(4,905	)
Shares issued at December 31, 2013	70,117		357,882		209,882	279,999		504,276	1	3		1,422,160
Stock transfers(1)	293,023		(13,023	)	—	(279,999	)	—	—	(1	)	—
Restricted stock issuance	15,278		—		—	—		—	—	—		15,278
Restricted stock repurchased	(2,025	)	—		—	—		—	—	—		(2,025	)
Restricted stock forfeited	(11,497	)	—		—	—		—	—	—		(11,497	)
Shares issued at December 31, 2014	364,896		344,859		209,882	—		504,276	1	2		1,423,916

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(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”) on 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.