Unaudited Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings Substantially Restricted	Accumulated Other Comprehensive Income
Balance, beginning, shares at Dec. 31, 2014		75,026,092
Balance, beginning at Dec. 31, 2014	$ 1,028,047	$ 750	$ 708,356	$ 301,197	$ 17,744
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, shares at Mar. 31, 2015		75,530,030
Balance, ending at Mar. 31, 2015	$ 1,053,524	$ 755	719,506	315,236	18,027
Balance, beginning, shares at Dec. 31, 2015	76,086,288	76,086,288
Balance, beginning at Dec. 31, 2015	$ 1,076,650	$ 761	736,368	337,532	1,989
Net income	28,682			28,682
Comprehensive income, accumulated other comprehensive income	3,332				3,332
Comprehensive income, total	32,014
Cash dividends declared	(15,281)			(15,281)
Stock issuances under stock incentive plans, shares		82,100
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock-based compensation and related taxes	$ 297		297
Balance, ending, shares at Mar. 31, 2016	76,168,388	76,168,388
Balance, ending at Mar. 31, 2016	$ 1,093,680	$ 762	$ 736,664	$ 350,933	$ 5,321