Consolidated Statements of Stockholders' Equity (USD $)	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at January 1, 2010 at Dec. 31, 2009	$ 170,555,000	$ 137,000	$ 130,867,000	$ 197,140,000	$ 27,080,000	$ 525,779,000
Balance at January 1, 2010 (in Shares) at Dec. 31, 2009	10,841,062	13,717,701
Net income				52,695,000		52,695,000
Other comprehensive income					9,207,000	9,207,000
Stock-based compensation			321,000			321,000
Tax benefit (expense) from exercise of stock options			154,000			154,000
Shares sold – options exercised		1,000	2,654,000			2,655,000
Shares sold – options exercised (in Shares)		102,349				(72,149)
Shares repurchased		(2,000)	(5,942,000)			(5,944,000)
Shares repurchased (in Shares)		(182,900)
Shares issued in conversion of preferred stock to common stock	(7,000)		7,000
Shares issued in conversion of preferred stock to common stock (in Shares)	(454)	108
Dividends declared to preferred stockholders				(8,673,000)		(8,673,000)
Dividends declared to common stockholders				(15,048,000)		(15,048,000)
Balance at Dec. 31, 2010	170,548,000	136,000	128,061,000	226,114,000	36,287,000	561,146,000
Balance (in Shares) at Dec. 31, 2010	10,840,608	13,637,258
Net income				64,072,000		64,072,000
Other comprehensive income					415,000	415,000
Stock-based compensation			2,751,000			2,751,000
Tax benefit (expense) from exercise of stock options			(52,000)			(52,000)
Shares sold – options exercised		2,000	8,390,000			8,392,000
Shares sold – options exercised (in Shares)		224,969				(224,969)
Shares issued in conversion of preferred stock to common stock	(33,000)		33,000
Shares issued in conversion of preferred stock to common stock (in Shares)	(2,118)	511
Dividends declared to preferred stockholders				(8,671,000)		(8,671,000)
Dividends declared to common stockholders				(16,317,000)		(16,317,000)
Balance at Dec. 31, 2011	170,515,000	138,000	139,183,000	265,198,000	36,702,000	611,736,000
Balance (in Shares) at Dec. 31, 2011	10,838,490	13,862,738
Net income				57,957,000		57,957,000
Other comprehensive income					14,106,000	14,106,000
Stock-based compensation			2,366,000			2,366,000
Tax benefit (expense) from exercise of stock options			(267,000)			(267,000)
Shares sold – options exercised		3,000	13,409,000			13,412,000
Shares sold – options exercised (in Shares)		295,371				(295,371)
Shares issued in conversion of preferred stock to common stock	(1,000)		1,000
Shares issued in conversion of preferred stock to common stock (in Shares)	(78)	18
Dividends declared to preferred stockholders				(8,671,000)		(8,671,000)
Dividends declared to common stockholders				(30,967,000)		(30,967,000)
Balance at Dec. 31, 2012	$ 170,514,000	$ 141,000	$ 154,692,000	$ 283,517,000	$ 50,808,000	$ 659,672,000
Balance (in Shares) at Dec. 31, 2012	10,838,412	14,158,127