Condensed Financial Information (Parent Company Only) (Details 2) (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
Condensed Statements of Comprehensive Income
Net Income	$ 5,170	$ 4,850	$ 4,910	$ 4,613	$ 3,522	$ 3,417	$ 3,093	$ 2,765	$ 19,543	$ 12,797	$ 10,455
Other Comprehensive Income (Loss)
Change in fair value of derivative instruments, net of taxes									(376)	(2,300)	(1,172)
Unrealized appreciation (depreciation) on available-for-sale securities, net of taxes									1,636	8,949	(1,853)
Less: reclassification adjustment for realized gains included in net income, net of taxes of $1 for 2012, $622 for 2011 and $187 for 2010, respectively									1	1,155	346
Other Comprehensive Income									1,259	5,494	(3,371)
Comprehensive Income									20,802	18,291	7,084
Parent Company [Member]
Condensed Statements of Comprehensive Income
Net Income									19,543	12,797	10,455
Other Comprehensive Income (Loss)
Change in fair value of derivative instruments, net of taxes									(376)	(2,300)	(1,172)
Unrealized appreciation (depreciation) on available-for-sale securities, net of taxes									1,636	8,949	(1,853)
Less: reclassification adjustment for realized gains included in net income, net of taxes of $1 for 2012, $622 for 2011 and $187 for 2010, respectively									1	1,155	346
Other Comprehensive Income									1,259	5,494	(3,371)
Comprehensive Income									$ 20,802	$ 18,291	$ 7,084