Summary of Significant Accounting Policies (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income attributed to:
Total	$ 15,790	$ 9,413	$ 11,870	$ 11,806	$ 11,294	$ 10,479	$ 9,015	$ 11,494	$ 48,879	$ 42,282	$ 22,429
Common stock [Member]
Net income attributed to:
Total									48,853	42,040	22,061
Participating restricted stock [Member]
Net income attributed to:
Total									$ 26	$ 242	$ 368