Consolidated Statements of Stockholders’ Equity (June 30, 2012 and 2013 Unaudited) (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2011	$ 172	$ 112,436	$ 439	$ 294,864	$ 407,911
Comprehensive income:
Net income				12,891	12,891
Change in unrealized appreciation on available-for-sale securities, net of income taxes			62		62
Comprehensive income					12,953
Stock issued as bonus shares	1	191			192
Vesting bonus shares		718			718
Stock issued for employee stock purchase plan		132			132
Stock granted under stock-based compensation plans		51			51
Repurchase of common stock	(3)	(7,703)			(7,706)
Cash Dividends				(6,838)	(6,838)
Balance at Jun. 30, 2012	170	105,825	501	300,917	407,413
Balance at Dec. 31, 2011	172	112,436	439	294,864	407,911
Comprehensive income:
Net income				14,793	14,793
Change in unrealized appreciation on available-for-sale securities, net of income taxes			(244)		(244)
Comprehensive income					14,549
Stock issued as bonus shares	(1)				(1)
Vesting bonus shares		587			587
Stock granted under stock-based compensation plans		32			32
Repurchase of common stock	(4)	(9,857)			(9,861)
Cash Dividends				(6,657)	(6,657)
Balance at Dec. 31, 2012	165	96,587	257	309,053	406,062
Comprehensive income:
Net income				12,513	12,513
Change in unrealized appreciation on available-for-sale securities, net of income taxes			(2,667)		(2,667)
Comprehensive income					9,846
Stock issued as bonus shares	1	228			229
Vesting bonus shares		687			687
Stock issued for employee stock purchase plan		126			126
Exercise of stock options – 4,000 shares		95			95
Stock granted under stock-based compensation plans		27			27
Repurchase of common stock	(3)	(8,316)			(8,319)
Cash Dividends				(6,903)	(6,903)
Balance at Jun. 30, 2013	$ 163	$ 89,434	$ (2,410)	$ 314,663	$ 401,850