Earnings Per Share (Details) (USD $) In Thousands, except 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, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic and Diluted Earnings Per Share
Net Income	$ 20,758	$ 19,444	$ 18,981	$ 16,333	$ 14,348	$ (19,048)	$ 11,886	$ 10,285	$ 75,516	$ 17,471	$ 42,330
Average outstanding shares - basic									71,928,570	71,915,073	69,657,980
Add: dilutive stock options									86		2,365
Average outstanding shares - diluted									71,928,656	71,915,073	69,660,345
Basic earnings per share	$ 0.29	$ 0.27	$ 0.26	$ 0.23	$ 0.20	$ (0.27)	$ 0.17	$ 0.14	$ 1.05	$ 0.24	$ 0.61
Diluted earnings per share	$ 0.29	$ 0.27	$ 0.26	$ 0.23	$ 0.20	$ (0.27)	$ 0.17	$ 0.14	$ 1.05	$ 0.24	$ 0.61
Earnings Per Share (Textual) [Abstract]
Exclusion of Diluted average outstanding shares from calculation									879,525	1,567,561	2,295,424
Retained Earnings [Member]
Basic and Diluted Earnings Per Share
Net Income									$ 75,516	$ 17,471	$ 42,330