Parent Company Financial Statements (Statements of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 35,074	$ 29,724	$ 24,051
Adjustments to reconcile net income to net cash provided by operating activities:
(Increase) decrease in other assets	(7,987)	(2,804)	646
Net cash provided by operating activities	5,467	37,199	30,439
Net cash provided by (used in) investing activities	25,337	(158,576)	10,149
Cash flows from financing activities:
Issuance of treasury stock, including net deferred compensation plan activity	0	0	44
Proceeds from the issuance of common stock under dividend reinvestment plan	0	754	1,002
Proceeds from the exercise of stock options and issuance of other compensation-related equity instruments	1,257	885	785
Tax benefit (expense) from stock option exercises and issuance of other compensation-related equity instruments	210	115	65
Cash dividends paid	(15,133)	(14,205)	(13,582)
Net cash (used in) provided by financing activities	(25,174)	115,661	(5,112)
Net increase (decrease) in cash and cash equivalents	5,630	(5,716)	35,476
Cash and cash equivalents at beginning of year	87,020	92,736	57,260
Cash and cash equivalents at end of year	92,650	87,020	92,736
Parent Company [Member]
Cash flows from operating activities:
Net income	35,074	29,724	24,051
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries	20,177	16,557	10,190
(Increase) decrease in dividend receivable	(298)	(660)	360
(Increase) decrease in other assets	77	(246)	(373)
Increase (decrease) in accrued expenses and other liabilities	(215)	281	(92)
Other, net	(237)	(115)	(109)
Net cash provided by operating activities	14,224	12,427	13,647
Net cash provided by (used in) investing activities	0	0	0
Cash flows from financing activities:
Issuance of treasury stock, including net deferred compensation plan activity	0	0	44
Proceeds from the issuance of common stock under dividend reinvestment plan	0	754	1,002
Proceeds from the exercise of stock options and issuance of other compensation-related equity instruments	1,257	885	785
Tax benefit (expense) from stock option exercises and issuance of other compensation-related equity instruments	210	115	65
Cash dividends paid	(15,133)	(14,205)	(13,582)
Net cash (used in) provided by financing activities	(13,666)	(12,451)	(11,686)
Net increase (decrease) in cash and cash equivalents	558	(24)	1,961
Cash and cash equivalents at beginning of year	3,106	3,130	1,169
Cash and cash equivalents at end of year	$ 3,664	$ 3,106	$ 3,130