Quarterly Financial Data (Unaudited) (Details Textual) (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
Quarterly Financial Data (Textual) [Abstract]
Income before income taxes	$ 12,674	$ 9,003	$ 4,033	$ 11,433	$ 9,517	$ 5,518	$ 4,832	$ 7,490	$ 37,143	$ 27,357	$ 44,222
Net income	9,226	7,121	3,445	9,561	8,073	4,884	4,594	6,630	29,353	24,181	34,520
Comprehensive income	8,091	8,570	3,948	9,508	8,046	6,162	5,386	6,537	30,117	26,131	32,057
As Reported [Member]
Quarterly Financial Data (Textual) [Abstract]
Income before income taxes					9,494	5,498	4,793	7,486		27,271	44,354
Net income					8,058	4,871	4,569	6,627		24,125	34,606
Comprehensive income					8,031	6,149	5,360	6,535		26,075	32,143
Scenario Adjustment [Member]
Quarterly Financial Data (Textual) [Abstract]
Adjustment Income before income taxes					23	20	39	4
Adjustment Net income					15	13	25	3
Adjustment Comprehensive income					$ 15	$ 13	$ 26	$ 2