Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 18,892	$ 20,157	$ 38,374	$ 38,364
Weighted average shares outstanding - basic	5,107,415	5,106,351	5,107,199	5,106,144
Weighted average shares - diluted	5,107,415	5,106,351	5,107,199	5,106,144
Net income per common share - basic	$ 3.70	$ 3.95	$ 7.51	$ 7.51
Net income per common share - diluted	$ 3.70	$ 3.95	$ 7.51	$ 7.51