CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2008	$ 33,468	$ 212,400	$ 329,914	$ (12,864)	$ (18,267)	$ 544,651
Balance (in shares) at Dec. 31, 2008	32,633,404
Net income			41,445			41,445
Other comprehensive income, net of tax				4,080		4,080
Dividends declared:
Common			(28,820)			(28,820)
Common stock issued under employee stock plan, including tax benefits	163	981			97	1,241
Common stock issued under employee stock plan, including tax benefits (in shares)	166,904
Stock-based compensation		3,100				3,100
Balance at Dec. 31, 2009	33,631	216,481	342,539	(8,784)	(18,170)	565,697
Balance (in shares) at Dec. 31, 2009	32,800,308
Net income			63,320			63,320
Other comprehensive income, net of tax				(556)		(556)
Dividends declared:
Common			(31,159)			(31,159)
Common stock issued under employee stock plan, including tax benefits	500	5,539			394	6,433
Common stock issued under employee stock plan, including tax benefits (in shares)	518,635
Stock-based compensation		3,523				3,523
Balance at Dec. 31, 2010	34,131	225,543	374,700	(9,340)	(17,776)	607,258
Balance (in shares) at Dec. 31, 2010	33,318,943
Net income			73,142			73,142
Other comprehensive income, net of tax				38,505		38,505
Dividends declared:
Common			(36,037)			(36,037)
Common stock issued under employee stock plan, including tax benefits	311	4,947			93	5,351
Common stock issued under employee stock plan, including tax benefits (in shares)	314,665
Stock-based compensation		3,784				3,784
Stock issued for acquisition	3,353	79,227				82,580
Stock issued for acquisition (in shares)	3,352,801
Balance at Dec. 31, 2011	$ 37,795	$ 313,501	$ 411,805	$ 29,165	$ (17,683)	$ 774,583
Balance (in shares) at Dec. 31, 2011	36,986,409