Shareholders' equity (Details 3) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Stock options
Class of Stock
Vesting period	4 years
Expiration period	10 years
Restricted stock units
Class of Stock
Vesting period	4 years
Expiration period	10 years
2012 Equity Incentive Plan | Stock options
Stock Options
Outstanding at beginning of the period (in shares)	1,190,000	700,000
Granted (in shares)	1,220,000
Exercised (in shares)	(28,750)
Forfeited (in shares)	(216,250)	(30,000)
Outstanding at end of the period (in shares)	2,165,000	670,000
Exercisable at end of the period (in shares)	131,250
Weighted Average Exercise Price
Outstanding at beginning of the period (in dollars per share)	$ 15.48	$ 15.00
Granted (in dollars per share)	$ 16.74
Exercised (in dollars per share)	$ 15.00
Forfeited (in dollars per share)	$ 15.70	$ 15.00
Outstanding at end of the period (in dollars per share)	$ 16.17	$ 15.00
Exercisable at end of the period (in dollars per share)	$ 15.00
2012 Equity Incentive Plan | Restricted stock units
Class of Stock
Granted (in shares)	92,000