Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Net Income Per Share
Net income	$ 9,255	$ 8,177
Average shares outstanding, basic	14,647	14,506
Dilutive securities (in shares)	205	195
Average shares outstanding including dilutive securities	14,852	14,701
Net income per share, basic (in dollars per share)	$ 0.63us-gaap_EarningsPerShareBasic	$ 0.56us-gaap_EarningsPerShareBasic
Net income per share, diluted (in dollars per share)	$ 0.62us-gaap_EarningsPerShareDiluted	$ 0.56us-gaap_EarningsPerShareDiluted

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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