Condensed Consolidated Statements of Shareholders' Equity (unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common stock [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]
Balance at Dec. 31, 2011	$ 170,820	$ 84,564	$ 83,107	$ 3,149
Balance (in shares) at Dec. 31, 2011		15,398
Comprehensive income:
Net income	12,258	0	12,258	0
Other comprehensive income (loss), net	2,471	0	0	2,471
Cash dividends on common stock	(5,399)	0	(5,399)	0
Stock-based compensation expense	591	591	0	0
Issuance of common stock under stock plans	205	205	0	0
Issuance of common stock under stock plans (in shares)		53
Tax benefit associated with stock awards	21	21	0	0
Balance at Sep. 30, 2012	180,967	85,381	89,966	5,620
Balance (in shares) at Sep. 30, 2012		15,451
Balance at Dec. 31, 2012	182,624	85,707	92,234	4,683
Balance (in shares) at Dec. 31, 2012	15,483,598	15,484
Comprehensive income:
Net income	11,994	0	11,994	0
Other comprehensive income (loss), net	(7,514)	0	0	(7,514)
Cash dividends on common stock	(6,046)	0	(6,046)	0
Stock-based compensation expense	680	680	0	0
Issuance of common stock under stock plans	56	56	0	0
Issuance of common stock under stock plans (in shares)		48
Tax benefit associated with stock awards	4	4	0	0
Balance at Sep. 30, 2013	$ 181,798	$ 86,447	$ 98,182	$ (2,831)
Balance (in shares) at Sep. 30, 2013	15,532,349	15,532