Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Comprehensive Income
Net income	$ 30,032	$ 22,595	$ 51,882
Unrealized gains on securities:
Unrealized holding gains (losses) arising during period	4,739	7,345	(1,323)
Tax effect	(1,793)	(2,647)	470
Reclassification adjustment for gains included in net income	(189)	(308)	(292)
Tax effect	72	111	105
Net of tax amount	2,829	4,501	(1,040)
Noncredit portion of other-than-temporary impairment losses:
Total other-than-temporary impairment losses		(115)	(1,281)
Tax effect		44	455
Reclassification adjustment of credit portion included in net income		115	6,770
Tax effect		(44)	(2,404)
Net of tax amount			3,540
Unrealized losses on derivative financial instruments qualifying as cash flow hedges:
Unrealized holding losses arising during period	(403)	(1,060)	(776)
Tax effect	153	428	276
Reclassification adjustment for losses included in interest expense	293	304	162
Tax effect	(112)	(123)	(58)
Net of tax amount	(69)	(451)	(396)
Change in pension and retiree medical plan obligation:
Change in pension and retiree medical plan obligation during period	610	(5,111)	(811)
Tax effect	(245)	2,104	297
Net of tax amount	365	(3,007)	(514)
Other comprehensive income, net of tax	3,125	1,043	1,590
Comprehensive income	$ 33,157	$ 23,638	$ 53,472