We calculate earnings per share in accordance with ASC subtopic 260-10, Earnings per Share, using the two-class method. The two-class method requires that share-based awards with non-forfeitable dividends be classified as participating securities. In calculating basic earnings per share, this method requires net income to be reduced by the amount of dividends declared in the period for each participating security and by the contractual amount of dividends or other participation payments that are paid or accumulated for the period. Undistributed earnings for the period are allocated to participating securities based on the contractual participation rights of the security to share in those current earnings assuming all earnings for the period are distributed. Recipients of certain of our restricted stock unit awards have contractual participation rights that are equivalent to those of common stockholders. Therefore, we allocate undistributed earnings to these restricted stock unit participating securities and common stock based on their respective participation percentage.

The two-class method also requires the denominator to include the weighted average number of shares of restricted stock units participating securities when calculating basic earnings per share. For the three and nine months ended September 30, 2011, there were 0.6 million and 0.8 million weighted average restricted stock units, participating securities, respectively, included in the denominator. For the three and nine months ended September 30, 2010, there were 1.0 million and 1.1 million weighted average restricted stock units participating securities, respectively, included in the denominator. Diluted earnings per share also include the additional share equivalents from the assumed conversion of stock based awards including options and certain restricted stock units. Conversion of stock options is calculated using the treasury stock method, subject to anti-dilution provisions

In computing diluted earnings per share for the three and nine months ended September 30, 2011, common stock equivalents of 0.3 million shares and 0.2 million shares, respectively, were not included due to their anti-dilutive effect. For the three and nine months ended September 30, 2010, all common stock equivalents were excluded due to their anti-dilutive effect.

Computations of basic and diluted earnings per share are presented in the following table:

		Three months ended September 30,				Nine months ended September 30,

In thousands, except per share data		2011		2010		2011		2010
Basic earnings per share
Undistributed income		$	34,358	$	24,958	$	61,073	$	27,617
Deduct: Undistributed earnings—Restricted stock units participating securities			611		699		1,414		876

Common stockholders' interest in undistributed income		$	33,747	$	24,259	$	59,659	$	26,741

Weighted average common shares—Basic			34,165		33,894		34,036		33,779
Total basic earnings per common share		$	0.99	$	0.72	$	1.75	$	0.79

Diluted earnings per share
Common stockholders' interest in undistributed income		$	33,747	$	24,259	$	59,659	$	26,741

Weighted average common shares—Basic			34,165		33,894		34,036		33,779
	Stock-based awards		46		—		29		—

Weighted average common shares—Diluted			34,211		33,894		34,065		33,779

Total diluted earnings per common share		$	0.99	$	0.72	$	1.75	$	0.79