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, 2013		74,373,296
Balance, beginning at Dec. 31, 2013	$ 963,250	$ 744	$ 690,918	$ 261,943	$ 9,645
Net income	84,701			84,701
Comprehensive income, accumulated other comprehensive income	13,030				13,030
Comprehensive income, total	97,731
Cash dividends declared	(37,410)			(37,410)
Stock issuances under stock incentive plans, shares		95,064
Stock issuances under stock incentive plans, value	758	$ 1	757
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	1,024		1,024
Balance, ending, shares at Sep. 30, 2014		75,024,092
Balance, ending at Sep. 30, 2014	$ 1,040,480	$ 750	707,821	309,234	22,675
Balance, beginning, shares at Dec. 31, 2014	75,026,092	75,026,092
Balance, beginning at Dec. 31, 2014	$ 1,028,047	$ 750	708,356	301,197	17,744
Net income	86,619			86,619
Comprehensive income, accumulated other comprehensive income	(9,737)				(9,737)
Comprehensive income, total	76,882
Cash dividends declared	(42,409)			(42,409)
Stock issuances under stock incentive plans, shares		62,346
Stock issuances under stock incentive plans, value	17	$ 1	16
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	$ 1,495		1,495
Balance, ending, shares at Sep. 30, 2015	75,532,082	75,532,082
Balance, ending at Sep. 30, 2015	$ 1,074,808	$ 755	$ 720,639	$ 345,407	$ 8,007