Parent Company Financial Statements (Statements of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 40,824	$ 36,153	$ 35,074
Adjustments to reconcile net income to net cash provided by operating activities:
(Increase ) decrease in other assets	7,192	(2,589)	7,987
Net cash provided by operating activities	2,693	80,850	5,467
Cash flows from investing activities:
Repayment of investment in capital trust	0	310	0
Net cash (used in) provided by investing activities	(357,372)	(184,062)	25,337
Cash flows from financing activities:
Proceeds from stock option exercises and issuance of other equity instruments	1,189	3,681	1,257
Tax benefit from stock option exercises and other equity instruments	578	570	210
Redemption of junior subordinated debentures	0	(10,310)	0
Cash dividends paid	(19,722)	(16,628)	(15,133)
Net cash provided by (used in) financing activities	349,712	95,879	(25,174)
Net (decrease) increase in cash and cash equivalents	(4,967)	(7,333)	5,630
Cash and cash equivalents at beginning of year	85,317	92,650	87,020
Cash and cash equivalents at end of year	80,350	85,317	92,650
Parent Company [Member]
Cash flows from operating activities:
Net income	40,824	36,153	35,074
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries	(21,554)	(12,899)	(20,177)
Increase in dividend receivable	(495)	(408)	(298)
(Increase ) decrease in other assets	183	397	77
Decrease in accrued expenses and other liabilities	(516)	(621)	(215)
Other, net	(245)	(214)	(237)
Net cash provided by operating activities	18,197	22,408	14,224
Cash flows from investing activities:
Repayment of investment in capital trust	0	310	0
Net cash (used in) provided by investing activities	0	310	0
Cash flows from financing activities:
Issuance of treasury stock, including net deferred compensation plan activity	0	30	0
Proceeds from stock option exercises and issuance of other equity instruments	1,189	3,651	1,257
Tax benefit from stock option exercises and other equity instruments	578	570	210
Redemption of junior subordinated debentures	0	(10,310)	0
Cash dividends paid	(19,722)	(16,628)	(15,133)
Net cash provided by (used in) financing activities	(17,955)	(22,687)	(13,666)
Net (decrease) increase in cash and cash equivalents	242	31	558
Cash and cash equivalents at beginning of year	3,695	3,664	3,106
Cash and cash equivalents at end of year	$ 3,937	$ 3,695	$ 3,664