Condensed Parent Company Information (Condensed Balance Sheets) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash on deposit with bank subsidiary	$ 253,084,000	$ 223,274,000	$ 241,507,000	$ 216,167,000
Premises and equipment	75,113,000us-gaap_PropertyPlantAndEquipmentNet	77,448,000us-gaap_PropertyPlantAndEquipmentNet
Other assets	18,974,000us-gaap_OtherAssets	29,473,000us-gaap_OtherAssets
Total assets	3,218,383,000us-gaap_Assets	3,185,070,000us-gaap_Assets
Liabilities and shareholders' equity
Trust preferred securities	116,394,000us-gaap_OtherBorrowings	46,394,000us-gaap_OtherBorrowings
Other liabilities	17,698,000us-gaap_OtherLiabilities	14,856,000us-gaap_OtherLiabilities
Total liabilities	2,830,684,000us-gaap_Liabilities	2,813,148,000us-gaap_Liabilities
Total shareholders' equity	387,699,000us-gaap_StockholdersEquity	371,922,000us-gaap_StockholdersEquity	356,117,000us-gaap_StockholdersEquity	345,150,000us-gaap_StockholdersEquity
Total liabilities and shareholders' equity	3,218,383,000	3,185,070,000
Parent Company [Member]
Assets
Cash on deposit with bank subsidiary	4,272,000	4,208,000	3,335,000	3,324,000
Investment in wholly-owned subsidiaries, at equity	430,436,000	414,212,000
Premises and equipment	7,000	7,000
Other assets	1,641,000	1,659,000
Total assets	436,356,000	420,086,000
Liabilities and shareholders' equity
Trust preferred securities	46,394,000	46,394,000
Other liabilities	2,263,000	1,770,000
Total liabilities	48,657,000	48,164,000
Total shareholders' equity	387,699,000	371,922,000
Total liabilities and shareholders' equity	$ 436,356,000	$ 420,086,000

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