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, 2014		$ 15,504	$ 96,841	$ 492,776	$ 4,193
Shares issued, Value		58	1,316
Net income	$ 34,812			34,812
Net change	(1,741)				(1,741)
Tax effect of stock options			291
Dividends on common stock				(10,560)
Stock-based compensation arrangements			754
Balance at end of period at Jun. 30, 2015	634,244	15,562	99,202	517,028	2,452
Balance at beginning of period at Mar. 31, 2015		15,512	97,477	503,758	4,932
Shares issued, Value		50	1,080
Net income	18,553			18,553
Net change	(2,480)				(2,480)
Tax effect of stock options			355
Dividends on common stock				(5,283)
Stock-based compensation arrangements			290
Balance at end of period at Jun. 30, 2015	634,244	15,562	99,202	517,028	2,452
Balance at beginning of period at Dec. 31, 2015	655,510	15,597	102,865	535,521	1,527
Shares issued, Value		63	1,867
Net income	34,072			34,072
Net change	1,076				1,076
Tax effect of stock options			43
Dividends on common stock				(11,179)
Stock-based compensation arrangements			901
Shares acquired and canceled, Value		(100)		(5,423)
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
Net income	17,493			17,493
Net change	546				546
Tax effect of stock options			252
Dividends on common stock				(5,600)
Stock-based compensation arrangements			450
Balance at end of period at Jun. 30, 2016	$ 676,830	$ 15,560	$ 105,676	$ 552,991	$ 2,603