Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Percentage employer matches of the employee's percentage contribution matched.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Stockholders' Equity (Details Textuals) (USD $)	12 Months Ended
Stockholders' Equity (Details Textuals) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Contribution Benefit Plans Disclosures [Line Items]
Total compensation expense	$ 30,513,000	$ 33,003,000	$ 29,310,000
Employee Stock Purchase Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Maximum number of common stock shares authorized for issuance under Plan	11,900,000
Shares available for future awards	354,074
Employer contribution rate	75.00%
Total compensation expense	7,000,000	6,500,000	5,700,000
401(k) Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employer contribution rate	100.00%
Employer's matching contributions	$ 9,900,000	$ 9,000,000	$ 8,000,000
Maximum [Member] \| Employee Stock Purchase Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee contribution rate	10.00%
Maximum [Member] \| 401(k) Plan [Member]
Defined Contribution Benefit Plans Disclosures [Line Items]
Employee contribution rate	6.00%