Consolidated Statements of Changes in Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock	Paid-in Capital	Retained Earnings Substantially Restricted	Accumulated Other Comprehensive Income
Balance at Dec. 31, 2010	$ 838,204	$ 719	$ 643,894	$ 193,063	$ 528
Balance, shares at Dec. 31, 2010		71,915,073
Net income	17,471			17,471
Comprehensive income (loss), accumulated other comprehensive income	32,959				32,959
Comprehensive income (loss), total	50,430
Cash dividends declared	(37,395)			(37,395)
Stock-based compensation and related taxes	(1,012)		(1,012)
Balance at Dec. 31, 2011	850,227	719	642,882	173,139	33,487
Balance, shares at Dec. 31, 2011		71,915,073
Net income	75,516			75,516
Comprehensive income (loss), accumulated other comprehensive income	14,475				14,475
Comprehensive income (loss), total	89,991
Cash dividends declared	(38,124)			(38,124)
Stock-based compensation and related taxes	(1,468)		(1,468)
Stock issuances under stock incentive plans, shares		22,149
Stock issuances under stock incentive plans, value	323	0	323
Balance at Dec. 31, 2012	900,949	719	641,737	210,531	47,962
Balance, shares at Dec. 31, 2012	71,937,222	71,937,222
Net income	95,644			95,644
Comprehensive income (loss), accumulated other comprehensive income	(38,317)				(38,317)
Comprehensive income (loss), total	57,327
Cash dividends declared	(44,232)			(44,232)
Stock-based compensation and related taxes	(335)		(335)
Stock issuances under stock incentive plans, shares		292,942
Stock issuances under stock incentive plans, value	4,507	3	4,504
Stock issued in connection with acquisitions, shares		2,143,132
Stock issued in connection with acquisitions, value	45,034	22	45,012
Balance at Dec. 31, 2013	$ 963,250	$ 744	$ 690,918	$ 261,943	$ 9,645
Balance, shares at Dec. 31, 2013	74,373,296	74,373,296