Unaudited Condensed 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, beginning at Dec. 31, 2013	$ 963,250	$ 744	$ 690,918	$ 261,943	$ 9,645
Balance, beginning, shares at Dec. 31, 2013		74,373,296
Net income	26,730			26,730
Comprehensive income, accumulated other comprehensive income	5,643				5,643
Comprehensive income, total	32,373
Cash dividends declared	(11,942)			(11,942)
Stock issuances under stock incentive plans, shares		92,370
Stock issuances under stock incentive plans, value	1,037	1	1,036
Stock-based compensation and related taxes	242		242
Balance, ending at Mar. 31, 2014	984,960	745	692,196	276,731	15,288
Balance, ending, shares at Mar. 31, 2014		74,465,666
Balance, beginning at Dec. 31, 2014	1,028,047	750	708,356	301,197	17,744
Balance, beginning, shares at Dec. 31, 2014	75,026,092	75,026,092
Net income	27,670			27,670
Comprehensive income, accumulated other comprehensive income	283				283
Comprehensive income, total	27,953
Cash dividends declared	(13,631)			(13,631)
Stock issuances under stock incentive plans, shares		60,294
Stock issuances under stock incentive plans, value	(289)	1	(290)
Stock issued in connection with acquisitions, shares		443,644
Stock issued in connection with acquisitions, value	10,776	4	10,772
Stock-based compensation and related taxes	668		668
Balance, ending at Mar. 31, 2015	$ 1,053,524	$ 755	$ 719,506	$ 315,236	$ 18,027
Balance, ending, shares at Mar. 31, 2015	75,530,030	75,530,030