Stockholders' Equity (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee and non-employee stock option exercise data
Unrecognized compensation cost related to employee stock options	$ 0
Number of options exercised (in shares)	1,462,369	876,115	575,944
Cash received from options exercised	50,168	26,620	14,290
Total intrinsic value of options exercised	108,425	37,530	15,508
Tax benefits realized from options exercised	$ 30,845	$ 9,299	$ 3,054

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of share options (or share units) exercised during the current period.

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