Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$ 24,292us-gaap_NetIncomeLoss	$ 22,235us-gaap_NetIncomeLoss	$ 18,664us-gaap_NetIncomeLoss
Change in securities available-for-sale (AFS):
Unrealized holding gains (losses) on available-for-sale securities arising during the period	6,763	(6,309)	2,360
Reclassification adjustment for (gains) losses realized in income	(932)	(97)	(2,139)
Other-than-temporary impairment losses on AFS securities realized in income	0	337	5
Net unrealized gains (losses)	5,831	(6,069)	226
Income tax effect	(2,040)	2,124	(79)
Net of tax amount	3,791	(3,945)	147
Change in unrealized gain on postretirement benefit:
Net gain (loss) on defined benefit postretirement medical plan realized during the period	(377)	287	148
Net amortization and deferral	35	46	51
Net gain (loss) activity during the period	(342)	333	199
Income tax effect	120	(117)	(69)
Net of tax amount	(222)	216	130
Total other comprehensive income (loss)	3,569	(3,729)	277
Comprehensive income	$ 27,861us-gaap_ComprehensiveIncomeNetOfTax	$ 18,506us-gaap_ComprehensiveIncomeNetOfTax	$ 18,941us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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