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, 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 issuances under stock incentive plans, shares		22,149
Stock issuances under stock incentive plans, value	323	0	323
Stock-based compensation and related taxes	(1,468)		(1,468)
Balance at Dec. 31, 2012	900,949	719	641,737	210,531	47,962
Balance, shares at Dec. 31, 2012		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 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	45,033	22	45,011
Stock-based compensation and related taxes	(334)		(334)
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
Net income	112,755			112,755
Comprehensive income (loss), accumulated other comprehensive income	8,099				8,099
Comprehensive income (loss), total	120,854
Cash dividends declared	(73,501)			(73,501)
Stock issuances under stock incentive plans, shares		97,064
Stock issuances under stock incentive plans, value	784	1	783
Stock issued in connection with acquisitions, shares		555,732
Stock issued in connection with acquisitions, value	15,127	5	15,122
Stock-based compensation and related taxes	1,533		1,533
Balance at Dec. 31, 2014	$ 1,028,047	$ 750	$ 708,356	$ 301,197	$ 17,744
Balance, shares at Dec. 31, 2014	75,026,092	75,026,092