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	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
Balance, ending at Sep. 30, 2015	$ 1,074,808	$ 755	720,639	345,407	8,007
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	90,090			90,090
Comprehensive income, accumulated other comprehensive income	14,849				14,849
Comprehensive income, total	104,939
Cash dividends declared	(45,909)			(45,909)
Stock issuances under stock incentive plans, shares		89,569
Stock issuances under stock incentive plans, value	0	$ 1	(1)
Stock issued in connection with acquisitions, shares		349,545
Stock issued in connection with acquisitions, value	10,465	$ 3	10,462
Stock-based compensation and related taxes	$ 1,634		1,634
Balance, ending, shares at Sep. 30, 2016	76,525,402	76,525,402
Balance, ending at Sep. 30, 2016	$ 1,147,779	$ 765	$ 748,463	$ 381,713	$ 16,838