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, 2012		$ 15,242	$ 82,401	$ 415,607	$ 6,317
Shares issued		59	1,028
Net income	25,965			25,965
Net change	(2,092)				(2,092)
Tax effect of stock options			236
Dividends on common stock				(8,833)
Stock-based compensation arrangements			695
Shares acquired and canceled		(45)		(1,619)
Balance at end of period at Jun. 30, 2013	534,961	15,256	84,360	431,120	4,225
Balance at beginning of period at Mar. 31, 2013		15,228	82,956	423,637	5,886
Shares issued		50	870
Net income	12,593			12,593
Net change	(1,661)				(1,661)
Tax effect of stock options			213
Dividends on common stock				(4,411)
Stock-based compensation arrangements			321
Shares acquired and canceled		(22)		(699)
Balance at end of period at Jun. 30, 2013	534,961	15,256	84,360	431,120	4,225
Balance at beginning of period at Dec. 31, 2013	556,997	15,334	88,803	448,953	3,907
Shares issued		65	1,620
Net income	29,345			29,345
Net change	991				991
Tax effect of stock options			248
Dividends on common stock				(9,537)
Stock-based compensation arrangements			776
Balance at end of period at Jun. 30, 2014	580,505	15,399	91,447	468,761	4,898
Balance at beginning of period at Mar. 31, 2014		15,364	89,951	458,857	3,940
Shares issued		35	742
Net income	14,688			14,688
Net change	958				958
Tax effect of stock options			325
Dividends on common stock				(4,784)
Stock-based compensation arrangements			429
Balance at end of period at Jun. 30, 2014	$ 580,505	$ 15,399	$ 91,447	$ 468,761	$ 4,898