Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	COMMON STOCK [Member]	CAPITAL SURPLUS [Member]	RETAINED EARNINGS [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME [Member]
Balance at beginning of period at Dec. 31, 2015		$ 15,597	$ 102,865	$ 535,521	$ 1,527
Shares issued, Value		63	1,867
Shares acquired and canceled, Value		(100)		(5,423)
Tax effect of stock options			43
Stock-based compensation arrangements			901
Net income	$ 34,072			34,072
Dividends on common stock				(11,179)
Net change	1,076				1,076
Balance at end of period at Jun. 30, 2016	676,830	15,560	105,676	552,991	2,603
Balance at beginning of period at Mar. 31, 2016		15,528	103,978	541,098	2,057
Shares issued, Value		32	996
Tax effect of stock options			252
Stock-based compensation arrangements			450
Net income	17,493			17,493
Dividends on common stock				(5,600)
Net change	546				546
Balance at end of period at Jun. 30, 2016	676,830	15,560	105,676	552,991	2,603
Balance at beginning of period at Dec. 31, 2016	711,094	15,811	117,541	577,648	94
Shares issued, Value		98	3,343
Stock-based compensation arrangements			465
Net income	45,232			45,232
Dividends on common stock				(12,122)
Net change	352				352
Balance at end of period at Jun. 30, 2017	748,462	15,909	121,349	610,758	446
Balance at beginning of period at Mar. 31, 2017		15,891	120,435	593,631	(84)
Shares issued, Value		18	671
Stock-based compensation arrangements			243
Net income	23,182			23,182
Dividends on common stock				(6,055)
Net change	530				530
Balance at end of period at Jun. 30, 2017	$ 748,462	$ 15,909	$ 121,349	$ 610,758	$ 446