Parent Company Only Financial Information (Details 1) (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
Dividends from:
Income Before Income Taxes									$ 23,547	$ 20,633	$ 14,785
Income tax benefit									6,411	5,529	3,469
Net Income	3,890	4,563	4,336	4,347	3,869	4,067	3,891	3,277	17,136	15,104	11,316
Other Comprehensive Income:
Net change in unrealized gains/losses on available-for-sale securities, net of reclassification and tax									3,561	14,441	2,554
Change in actuarial gain, net of amortization and tax, for post-employment health care plan, net of tax									(349)	(485)	(245)
Change in fair value of interest rate swap agreements designated as a cash flow hedge, net of tax									(49)	(522)	(107)
Total other comprehensive income									3,163	13,434	2,202
Comprehensive Income									20,299	28,538	13,518
Parent Company [Member]
Dividends from:
Bank subsidiary									7,990	7,600	6,665
Non-bank subsidiaries											150
Other									208	146	165
Total income									8,198	7,746	6,980
Expenses									(1,457)	(1,410)	(1,383)
Income Before Income Taxes									6,741	6,336	5,597
Income tax benefit									438	443	426
Equity in undistributed net income of bank subsidiary									8,682	7,162	4,463
Equity in undistributed net income of non-bank subsidiaries									1,275	1,163	830
Net Income									17,136	15,104	11,316
Other Comprehensive Income:
Net change in unrealized gains/losses on available-for-sale securities, net of reclassification and tax									3,561	14,441	2,554
Change in actuarial gain, net of amortization and tax, for post-employment health care plan, net of tax									(349)	(485)	(245)
Change in fair value of interest rate swap agreements designated as a cash flow hedge, net of tax									(49)	(522)	(107)
Total other comprehensive income									3,163	13,434	2,202
Comprehensive Income									$ 20,299	$ 28,538	$ 13,518