4.	Earnings Per Common Share

We compute earnings per share in accordance with ASC Topic

260,

Earnings per Share

("ASC

260"

), which requires earnings per share for each class of stock to be calculated using the

two

-class method. The

two

-class method is an allocation of earnings between the holders of common stock and a company's participating security holders. Under the

two

-class method, earnings for the reporting period are allocated between common shareholders and other security holders based on their respective participation rights in undistributed earnings. Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents are participating securities and, therefore, are included in computing earnings per share pursuant to the

two

-class method.

Basic earnings per common share is computed by dividing income or loss available to common stockholders by the weighted average number of shares of basic common stock outstanding. Our unvested restricted stock are classified as participating securities in accordance with ASC

260.

Net income allocated to the holders of our unvested restricted stock is calculated based on the shareholders’ proportionate share of weighted average shares of common stock outstanding on an if-converted basis.

For purposes of determining diluted earnings per common share, basic earnings per common share is further adjusted to include the effect of potential dilutive common shares outstanding, including stock options, stock appreciation rights, performance share awards and unvested restricted stock using the more dilutive of either the

two

-class method or the treasury stock method. Under the

two

-class method of calculating diluted earnings per share, net income is reallocated to common stock, unvested restricted stock and all dilutive securities based on the contractual participating rights of the security to share in the current earnings as if all of the earnings for the period had been distributed.

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
	(Dollars in thousands, except per share amounts)

Numerator:
Net income	$	98,994		$	112,760		$	181,614		$	185,421
Less: Net income allocated to unvested restricted stock		(408	)		(251	)		(705	)		(350	)
Net income available to common stockholders for basic earnings per common share		98,586			112,509			180,909			185,071
Effect of dilutive securities:
Interest on 1.625% convertible senior notes due 2018		94			91			468			453
Interest on 0.25% convertible senior notes due 2019		85			82			423			410
Interest on 1.25% convertible senior notes due 2032		64			62			320			310
Net income available to common stock for diluted earnings per share	$	98,829		$	112,744		$	182,120		$	186,244

Denominator:
Weighted average basic common shares outstanding		113,689,435			118,419,937			114,086,136			119,617,438
Effect of dilutive securities:
Share-based awards		821,628			583,264			868,491			575,516
1.625% convertible senior notes due 2018		7,171,943			7,163,865			7,171,943			7,163,865
0.25% convertible senior notes due 2019		3,641,157			3,637,091			3,641,157			3,637,091
1.25% convertible senior notes due 2032		6,312,249			6,283,989			6,312,249			6,283,989
Weighted average diluted shares outstanding		131,636,412			136,088,146			132,079,976			137,277,899

Income per common share:
Basic	$	0.87		$	0.95		$	1.59		$	1.55
Diluted	$	0.75		$	0.83		$	1.38		$	1.36