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 (Loss)/Income [Member]	Treasury Stock [Member]	Total
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, per share			(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, per share			(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
Net income			77,068			77,068
Other comprehensive income, net of tax				25,169		25,169
Dividends declared:
Common, per share			(41,855)			(41,855)
Common stock issued under employee stock plan, including tax benefits	496	8,457			275	9,228
Common stock issued under Employee stock plan, including tax benefits (in shares)	509,724
Stock-based compensation		3,668				3,668
Common stock issuance	2,130	52,787				54,917
Common stock issuance (in shares)	2,129,800
Balance at Dec. 31, 2012	$ 40,421	$ 378,413	$ 447,018	$ 54,334	$ (17,408)	$ 902,778
Balance (in shares) at Dec. 31, 2012	39,625,933