Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Common Class A [Member]
Numerator:
Allocation of net income	$ 5,170	$ 6,390
Denominator:
Weighted-average shares outstanding	20,066,755	19,996,285
Basic net income per share	$ 0.26	$ 0.32
Numerator:
Allocation of net income	5,170	6,390
Denominator:
Number of shares used in basic computation	20,066,755	19,996,285
Weighted-average shares effect of dilutive securities
Add: Director and employee stock options	291,477	364,836
Number of shares used in per share computations	20,358,232	20,361,121
Diluted net income per share	$ 0.25	$ 0.31
Common Class B [Member]
Numerator:
Allocation of net income	1,305	1,620
Denominator:
Weighted-average shares outstanding	5,576,775	5,576,775
Basic net income per share	$ 0.23	$ 0.29
Numerator:
Allocation of net income	$ 1,305	$ 1,620
Denominator:
Number of shares used in basic computation	5,576,775	5,576,775
Weighted-average shares effect of dilutive securities
Number of shares used in per share computations	5,576,775	5,576,775
Diluted net income per share	$ 0.23	$ 0.29

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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