Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 7,005	$ 5,579	$ 20,237	$ 17,901
Unrealized gains (losses) on securities available for sale:
Unrealized holding gains (losses) arising during the period, pretax	589	(47)	(154)	1,004
Tax (expense) benefit	(231)	$ 19	60	(391)
Reclassification to realized (gains) losses	$ 1		$ 1	(786)
Tax expense (benefit)				306
Postretirement Plans:
Amortization of unrecognized net actuarial (gain) loss	$ (16)	$ (56)	$ (63)	(166)
Tax expense (benefit)	6	(2)	24	65
Other comprehensive income (loss)	349	(86)	(132)	32
Comprehensive income	$ 7,354	$ 5,493	$ 20,105	$ 17,933