Schedule of status of options, and changes during the period (Details) (Class A common shares, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
2000 and 2004 stock option plans | Share options
Number of shares subject to options
Options granted in period (in shares)	0	0
Options exercised in period (in shares)	77,294	4,206
Options forfeited and expired in period (in shares)	113,356	57,194
Outstanding at the end of the period (in shares)	286,800	477,450	538,850
Exercisable at the end of the period (in shares)	286,800
Weighted average exercise price
Outstanding at the end of the period (in dollars per share)	$ 29.91	$ 23.44	$ 23.05
Options granted in period, weighted average exercise price (in dollars per share)	$ 0.00	$ 0.00
Options exercised in period, weighted average exercise price (in dollars per share)	$ 5.89	$ 5.89
Options forfeited and expired in period, weighted average exercise price (in dollars per share)	$ 19.03	$ 21.09
Exercisable at the end of the period (in dollars per share)	$ 29.91
Weighted average remaining contractual life
Outstanding, weighted average remaining contractual life	3 years 6 months
Exercisable, weighted average remaining contractual life	3 years 6 months
Aggregate intrinsic value
Outstanding, aggregate intrinsic value	$ 807
Exercisable, aggregate intrinsic value	807
2009 share award and incentive plan | Share options
Number of shares subject to options
Options granted in period (in shares)	756,650	811,450
Options exercised in period (in shares)	236,322	29,477
Options forfeited and expired in period (in shares)	702,178	364,223
Outstanding at the end of the period (in shares)	2,771,500	2,953,350	2,535,600
Exercisable at the end of the period (in shares)	526,750
Weighted average exercise price
Outstanding at the end of the period (in dollars per share)	$ 10.67	$ 9.54	$ 9.35
Options granted in period, weighted average exercise price (in dollars per share)	$ 13.26	$ 10.09
Options exercised in period, weighted average exercise price (in dollars per share)	$ 8.77	$ 8.44
Options forfeited and expired in period, weighted average exercise price (in dollars per share)	$ 8.57	$ 9.55
Exercisable at the end of the period (in dollars per share)	$ 9.79
Weighted average remaining contractual life
Outstanding, weighted average remaining contractual life	8 years 3 months 18 days
Exercisable, weighted average remaining contractual life	6 years 4 months 24 days
Aggregate intrinsic value
Outstanding, aggregate intrinsic value	12,309
Exercisable, aggregate intrinsic value	7,959
2009 share award and incentive plan | Deferred compensation
Aggregate intrinsic value
Outstanding, aggregate intrinsic value	$ 17,323