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	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
Balance, ending at Jun. 30, 2015	$ 1,056,451	$ 755	720,073	330,183	5,440
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	59,133			59,133
Comprehensive income, accumulated other comprehensive income	18,424				18,424
Comprehensive income, total	77,557
Cash dividends declared	(30,560)			(30,560)
Stock issuances under stock incentive plans, shares		85,292
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock-based compensation and related taxes	$ 1,012		1,012
Balance, ending, shares at Jun. 30, 2016	76,171,580	76,171,580
Balance, ending at Jun. 30, 2016	$ 1,124,659	$ 762	$ 737,379	$ 366,105	$ 20,413