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	55,407			55,407
Comprehensive income, accumulated other comprehensive income	14,561				14,561
Comprehensive income, total	69,968
Cash dividends declared	(24,629)			(24,629)
Stock issuances under stock incentive plans, shares		94,612
Stock issuances under stock incentive plans, value	764	$ 1	763
Stock-based compensation and related taxes	662		662
Balance, ending, shares at Jun. 30, 2014		74,467,908
Balance, ending at Jun. 30, 2014	$ 1,010,015	$ 745	692,343	292,721	24,206
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	57,005			57,005
Comprehensive income, accumulated other comprehensive income	(12,304)				(12,304)
Comprehensive income, total	44,701
Cash dividends declared	(28,019)			(28,019)
Stock issuances under stock incentive plans, shares		61,522
Stock issuances under stock incentive plans, value	(299)	$ 1	(300)
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	$ 1,245		1,245
Balance, ending, shares at Jun. 30, 2015	75,531,258	75,531,258
Balance, ending at Jun. 30, 2015	$ 1,056,451	$ 755	$ 720,073	$ 330,183	$ 5,440