Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2011

Stockholders' Equity

Schedule of stock option activity

	2009					2010
	Options			Weighted Average Exercise Price		Options			Weighted Average Exercise Price
Outstanding, beginning of period		4,668,490		$	39.82		5,185,091		$	38.19
Granted		1,326,694			33.00		951,072			42.70
Forfeited		(732,846	)		39.68		(332,105	)		40.66
Exercised		(77,247	)		33.38		(2,028,472	)		37.89
Outstanding, end of period		5,185,091		$	38.19		3,775,586		$	39.27

	2011
	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, beginning of period		3,775,586		$	39.27
Granted		1,217,958			49.30
Forfeited		(86,986	)		42.13
Exercised		(1,065,325	)		38.34
Outstanding, end of period		3,841,233		$	42.65		7.47	$	26,446
Vested and expected to vest at end of period		3,763,158		$	42.55		7.44	$	26,251
Exercisable, end of period		1,720,871		$	40.02		6.03	$	16,268

Schedule of weighted average assumptions used to determine weighted average grant date fair value

	2009			2010			2011
Risk-free interest rate		1.67	%		1.74	%		1.63	%
Expected life		4 years			4 years			4 years
Expected volatility		30.20	%		31.70	%		29.88	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Schedule of nonvested restricted stock award activity

	2009					2010					2011
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Outstanding, beginning of period		321,935		$	42.92		28,910		$	30.27		22,309		$	39.23
Awarded		30,385			30.36		22,309			39.23		18,748			52.11
Vested		(319,547	)		42.97		(28,910	)		30.27		(22,309	)		39.23
Forfeited		(3,863	)		36.66		—			—		—			—
Outstanding, ending of period		28,910		$	30.27		22,309		$	39.23		18,748		$	52.11

Schedule of nonvested restricted stock units

	2009					2010					2011
	Shares			Weighted Grant Date Fair Value		Shares			Weighted Grant Date Fair Value		Shares			Weighted Grant Date Fair Value
Outstanding, beginning of period		176,112		$	38.72		184,454		$	34.99		190,488		$	38.43
Awarded		121,065			32.91		101,812			42.75		115,003			49.14
Vested		(73,465	)		39.16		(84,615	)		36.20		(90,853	)		37.50
Forfeited		(39,258	)		37.60		(11,163	)		37.97		(8,300	)		42.94
Outstanding, ending of period		184,454		$	34.99		190,488		$	38.43		206,338		$	44.63

Computation of basic and diluted earnings per share

	2009		2010		2011
Numerator:
Net income	$	106,671	$	138,659	$	129,623
Denominator:
Weighted average number of common shares outstanding—basic		35,248		33,779		30,478
Common stock equivalents—stock options		46		448		480
Common stock equivalents—warrants		52		116		—
Common stock equivalents—restricted stock awards		29		12		9
Common stock equivalents—restricted stock units		41		86		91
Weighted average number of common shares outstanding—diluted		35,416		34,441		31,058
Net income per common share—basic	$	3.03	$	4.10	$	4.25
Net income per common share—diluted	$	3.01	$	4.03	$	4.17