CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Shareholders' equity
Preferred share capital, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred share capital, authorized (in shares)	50,000,000	50,000,000
Preferred share capital, issued (in shares)	0.00	0.00
Class A [Member]
Shareholders' equity
Ordinary share capital, par value (in dollars per share)	$ 0.10	$ 0.10
Ordinary share capital, authorized (in shares)	100,000,000	100,000,000
Ordinary share capital, issued (in shares)	30,423,704	30,283,200
Ordinary share capital, outstanding (in shares)	30,423,704	30,283,200
Class B [Member]
Shareholders' equity
Ordinary share capital, par value (in dollars per share)	$ 0.10	$ 0.10
Ordinary share capital, authorized (in shares)	25,000,000	25,000,000
Ordinary share capital, issued (in shares)	6,254,949	6,254,949
Ordinary share capital, outstanding (in shares)	6,254,949	6,254,949