Consolidated Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Retained Earnings	Common Stock In Treasury	Other Comprehensive Income (Loss)	Other Equity Transactions
Beginning balances at Dec. 31, 2011	$ 405,982	$ 185,913	$ 408,380	$ (118,279)	$ (72,215)	$ 2,183
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,664		24,664
Other comprehensive income	(16,214)				(16,214)
Cash dividends declared	(4,650)		(4,650)
Proceeds from exercise of 16, 74, and 68 shares under option plans for the years ended 2011, 2012 and 2013, respectively	158	158
Proceeds from exercise of 16 shares under option plans	817	817
Repurchase of 132 and 6 shares for the years ended 2011 and 2012, respectively	(119)			(119)
Repurchase of 6 shares	5,889	5,889
Stock-based compensation expense	(1,608)	(1,608)
Shares withheld for employee taxes on equity awards	76			100		(24)
Ending balances at Dec. 31, 2012	414,995	191,169	428,394	(118,298)	(88,429)	2,159
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,707		19,707
Other comprehensive income	28,541				28,541
Cash dividends declared	(6,583)		(6,583)
Proceeds from exercise of 16, 74, and 68 shares under option plans for the years ended 2011, 2012 and 2013, respectively	1,163	1,163
Proceeds from exercise of 16 shares under option plans	711	711
Repurchase of 6 shares	5,741	5,741
Stock-based compensation expense	(1,208)	(1,208)
Shares withheld for employee taxes on equity awards	254			147		107
Ending balances at Dec. 31, 2013	463,321	197,576	441,518	(118,151)	(59,888)	2,266
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41,721		41,721
Other comprehensive income	(22,349)				(22,349)
Cash dividends declared	(6,962)		(6,962)
Proceeds from exercise of 16, 74, and 68 shares under option plans for the years ended 2011, 2012 and 2013, respectively	359	359
Proceeds from exercise of 16 shares under option plans	477	477
Repurchase of 132 and 6 shares for the years ended 2011 and 2012, respectively	(22,282)			(22,282)
Repurchase of 6 shares	5,446	5,446
Stock-based compensation expense	(1,754)	(1,754)
Shares withheld for employee taxes on equity awards	156			(505)		661
Ending balances at Dec. 31, 2014	$ 458,133	$ 202,104	$ 476,277	$ (140,938)	$ (82,237)	$ 2,927