Stockholders' Equity (Narrative) (Details) - USD ($)	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Employee Stock Purchase Plan
Stock-based compensation	$ 6,675,000	$ 5,093,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights	1/8 on the six month anniversary of the date of grant, and 1/48 each month thereafter for 42 months
Award Expiration Period	10 years
Weighted-average grant date fair value of stock options	$ 33.66
Intrinsic value of options exercised	$ 12,400,000	$ 13,700,000
Unrecognized compensation cost	$ 16,000,000
Weighted-average period in which cost is expected to be recognized	2 years 7 months 6 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period	3 years
Weighted-average period in which cost is expected to be recognized	2 years 18 days
Unrecognized compensation cost, restricted stock	$ 5,400,000
2002 Stock Incentive Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future option grants	800,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Expiration Period	6 months	6 months
Employee Stock Purchase Plan
Shares allowed to purchase in employee stock purchase plan	1,250
Offering period of shares in employee stock purchase plan	6 months
Percentage of purchase price of stock	85.00%
Discount rate	15.00%
Shares issued in period	2,654	2,230
Stock-based compensation	$ 36,000	$ 31,000
Shares available for future purchases	73,087
Shares issued under employee stock purchase plan	200,000
Volatility rate	36.00%	39.00%
Employee Stock Purchase Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from employee stock purchase plan	$ 5,300,000	$ 3,600,000
Tax benefit related to options exercised	$ 0
Certain Directors \| 2002 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period	1 year
Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period	4 years
Vesting Period One \| 2002 Stock Incentive Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period	6 months
Award Vesting Rights, Percentage	12.50%
Vesting Period Two \| 2002 Stock Incentive Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Period	42 months
Award Vesting Rights, Percentage	2.08%

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Employee Stock Purchase Plan [Abstract]

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Percentage of purchase price of stock.

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Number of shares to be repurchased in accordance with a policy to use treasury stock to satisfy share-award conversions.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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The total cash inflow associated with the amount received from holders to acquire the entity's shares under incentive and share awards, including stock option exercises. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest quantity of shares an employee can purchase under the plan per period.

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Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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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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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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of share instruments newly issued under a share-based compensation plan.

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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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