Net Income Per Share (Calculation of Net Income per Common Share (Detail) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 11,225,000us-gaap_NetIncomeLoss	$ 10,928,000us-gaap_NetIncomeLoss
Basic:
Basic weighted average EPS shares	24,928,000	24,999,000
Basic net income per share	$ 0.45us-gaap_EarningsPerShareBasic	$ 0.44us-gaap_EarningsPerShareBasic
Diluted:
Basic weighted average EPS shares	24,928,000	24,999,000
Dilutive common stock equivalents	121,000	125,000
Dilutive EPS shares	25,049,000	25,124,000
Diluted net income per share	$ 0.45us-gaap_EarningsPerShareDiluted	$ 0.43us-gaap_EarningsPerShareDiluted
Anti-dilutive shares	9,000	47,000

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The weighted average number of shares or units and dilutive common stock or unit equivalents outstanding in the calculation of proforma diluted earnings per share (earnings per unit), which is commonly presented in initial public offerings based on the terms of the offering.

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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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