Redeemable stock and stockholders' equity (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012 item	Dec. 31, 2011
Redeemable stock
Shares authorized		100,000
Common Stock
Shares authorized		200,000,000	200,000,000
Shares issued		22,130,996	22,020,694
Shares outstanding		22,130,996	22,020,694
Par value (in dollars per share)		$ 0.01	$ 0.01
Number of votes per share		1
Deferred Stock Plan
Maximum percentage of fully diluted equity capitalization entitled to be received		1.00%
Deferred stock units converted into common stock (in shares)	174,229
Series A Redeemable Convertible Preferred Stock
Redeemable stock
Shares authorized		65,000
Par value (in dollars per share)		$ 0.01
Dividend rate (as a percent)		10.00%
Dividend rate as a percentage of aggregate of all annual dividends that the holder of stock becomes entitled to receive, but which has not been declared or paid		10.00%
Redemption price per share (in dollars per share)		$ 1,000
Series B Redeemable Preferred Stock
Redeemable stock
Shares authorized		1
Par value (in dollars per share)		$ 0.01
Redemption price per share (in dollars per share)		$ 1,000
Number of directors that the holder is entitled to elect		4
Series C Redeemable Preferred Stock
Redeemable stock
Shares authorized		1
Par value (in dollars per share)		$ 0.01
Redemption price per share (in dollars per share)		$ 1,000
Number of directors that the holder is entitled to elect		2