Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]
Beginning balance at Dec. 31, 2011	$ 714,814	$ 479,973	$ 193,372	$ 41,469
Beginning balance, shares at Dec. 31, 2011		104,482
Repurchase of common stock	(54)	(54)
Repurchase of common stock, shares		(5)
Exercise of stock options	2,557	2,557
Exercise of stock options, shares		292
Tax benefit from exercise of stock options	194	194
Shares issued pursuant to stock-based compensation plan	2,039	2,039
Shares issued pursuant to stock-based compensation plan, shares		121
Cash dividends declared	(35,642)		(35,642)
Net earnings	77,280		77,280
Other comprehensive income (loss), net of tax	1,782			1,782
Ending balance at Dec. 31, 2012	762,970	484,709	235,010	43,251
Ending balance, shares at Dec. 31, 2012		104,890
Repurchase of common stock	(559)	(559)
Repurchase of common stock, shares		(42)
Exercise of stock options	4,517	4,517
Exercise of stock options, shares		428
Tax benefit from exercise of stock options	475	475
Shares issued pursuant to stock-based compensation plan	1,926	1,926
Shares issued pursuant to stock-based compensation plan, shares		94
Cash dividends declared	(40,469)		(40,469)
Net earnings	95,608		95,608
Other comprehensive income (loss), net of tax	(52,581)			(52,581)
Ending balance at Dec. 31, 2013	771,887	491,068	290,149	(9,330)
Ending balance, shares at Dec. 31, 2013		105,370
Repurchase of common stock	(5,474)	(5,474)
Repurchase of common stock, shares		(384)
Exercise of stock options	5,522	5,522
Exercise of stock options, shares	512	512
Tax benefit from exercise of stock options	1,116	1,116
Shares issued pursuant to stock-based compensation plan	2,988	2,988
Shares issued pursuant to stock-based compensation plan, shares		395
Cash dividends declared	(42,356)		(42,356)
Net earnings	104,021		104,021
Other comprehensive income (loss), net of tax	40,405			40,405
Ending balance at Dec. 31, 2014	$ 878,109	$ 495,220	$ 351,814	$ 31,075
Ending balance, shares at Dec. 31, 2014		105,893