Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Net income	$ 8,746	$ 4,221	$ 24,491	$ 12,438
Less: Net income allocated to participating securities	78		195
Net income available to common shareholders	$ 8,668	$ 4,221	$ 24,296	$ 12,438
Denominator:
Weighted average common shares outstanding	20,410,000	20,265,000	20,349,000	20,102,000
Weighted average dilutive securities (in shares)	776,000	776,000	785,000	883,000
Weighted average common shares outstanding, diluted	21,186,000	21,041,000	21,134,000	20,985,000
Earnings per share
Income per common share, basic (in dollars per share)	$ 0.42	$ 0.21	$ 1.19	$ 0.62
Income per common share, diluted (in dollars per share)	$ 0.41	$ 0.20	$ 1.15	$ 0.59
Employee stock options
Earnings Per Share
Anti-dilutive shares excluded from the diluted earnings per share calculation (in shares)	229,000	90,000	229,000	90,000
Nonvested performance shares
Earnings Per Share
Anti-dilutive shares excluded from the diluted earnings per share calculation (in shares)	12,000	74,000	12,000	74,000