Earnings Per Common Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net Income attributed to:
Common stock	$ 11,870	$ 8,971	$ 23,651	$ 20,357
Participating restricted common stock		44	25	152
Net income	$ 11,870	$ 9,015	$ 23,676	$ 20,509