Quarterly Consolidated Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, 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, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Consolidated Financial Information (Unaudited)
Total revenue	$ 39,692	$ 37,506	$ 35,153	$ 35,739	$ 37,669	$ 39,480	$ 38,692	$ 40,812	$ 39,634	$ 40,191	$ 32,778	$ 35,699	$ 148,090	$ 156,653	$ 148,302
Net income	2,211	(7,194)	3,229	3,289	3,648	2,316	3,481	5,063	4,010	3,083	1,907	3,050	1,535	14,508	12,050
Net income (loss) attributable to common shareholders	$ (771)	$ (7,976)	$ 2,447	$ 2,507	$ 2,866	$ 1,534	$ 2,699	$ 4,281	$ 3,228	$ 2,301	$ 1,125	$ 2,268	$ (3,793)	$ 11,380	$ 8,922
Basic earnings (loss) per common share: (in dollars per share)	$ (0.09)	$ (0.94)	$ 0.29	$ 0.30	$ 0.34	$ 0.18	$ 0.33	$ 0.50	$ 0.37	$ 0.27	$ 0.13	$ 0.26	$ (0.45)	$ 1.35	$ 1.03
Diluted earnings (loss) per common share: (in dollars per share)	$ (0.09)	$ (0.91)	$ 0.28	$ 0.29	$ 0.33	$ 0.17	$ 0.31	$ 0.47	$ 0.35	$ 0.25	$ 0.12	$ 0.24	$ (0.43)	$ 1.28	$ 0.96
Average common shares outstanding (in shares)	8,277	8,667	8,585	8,404	8,425	8,397	8,322	8,552	8,654	8,683	8,729	8,660	8,490	8,423	8,681
Diluted average common shares outstanding (in shares)	8,525	8,889	8,848	8,756	8,758	8,811	8,796	9,048	9,199	9,080	9,255	9,303	8,791	8,876	9,251