Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	COMMON STOCK [Member]	CAPITAL SURPLUS [Member]	RETAINED EARNINGS [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME [Member]
Balance at beginning of period at Dec. 31, 2011		$ 15,118	$ 77,462	$ 381,017	$ 9,444
Balance at beginning of period, Shares at Dec. 31, 2011		15,117,430
Shares issued, Value		131	2,139
Shares issued, Shares		131,665
Net income	51,900			51,900
Net change	(3,127)				(3,127)
Tax effect of stock options			1,270
Dividends on common stock				(17,061)
Stock-based compensation arrangements			1,530
Shares acquired and canceled, Value		(7)		(249)
Shares acquired and canceled, Shares		(6,787)
Balance at end of period at Dec. 31, 2012	519,567	15,242	82,401	415,607	6,317
Balance at end of period, Shares at Dec. 31, 2012	15,242,308	15,242,308
Shares issued, Value		158	3,590
Shares issued, Shares		157,155
Net income	54,317			54,317
Net change	(2,410)				(2,410)
Tax effect of stock options			1,452
Dividends on common stock				(18,327)
Stock-based compensation arrangements			1,360
Shares acquired and canceled, Value		(66)		(2,644)
Shares acquired and canceled, Shares		(65,841)
Balance at end of period at Dec. 31, 2013	556,997	15,334	88,803	448,953	3,907
Balance at end of period, Shares at Dec. 31, 2013	15,333,622	15,333,622
Shares issued, Value		170	4,742
Shares issued, Shares		170,891
Net income	63,887			63,887
Net change	286				286
Tax effect of stock options			1,620
Dividends on common stock				(20,064)
Stock-based compensation arrangements			1,676
Balance at end of period at Dec. 31, 2014	$ 609,314	$ 15,504	$ 96,841	$ 492,776	$ 4,193
Balance at end of period, Shares at Dec. 31, 2014	15,504,513	15,504,513