Represents the number of performance milestones on which vesting of awards is based.

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Represents the number of shares of common stock the holder is entitled to receive upon vesting for each restricted stock unit held.

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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.

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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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Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

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Risk-free interest rate assumption used in valuing an instrument.

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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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Percentage of vesting of share-based compensation awards.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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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Gross number of share options (or share units) granted during the period.

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No definition available.

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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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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No definition available.

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Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

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Number of shares issued during the period as a result of an employee stock purchase plan.

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

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Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended
Stock-Based Compensation (Details) (USD $)	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Employee Stock-Based Compensation Expense
Stock-based compensation expense (in dollars)	$ 4,300,000	$ 4,100,000	$ 8,600,000	$ 8,500,000
Weighted-average fair values and assumptions used in calculation of fair value
Dividend yield (as a percent)	0.00%	0.00%	0.00%	0.00%
Employee Stock Purchase Plan
Employee Stock Purchase Plan
Number of shares issued	101,701		101,701
Shares of common stock reserved for issuance under the ESPP	1,250,000		1,250,000
Shares available for issuance	849,355		849,355
Unrecognized compensation expense (in dollars)	528,000		528,000
Weighted-average period of recognition of unrecognized stock-based compensation expense			5 months
Weighted-average fair values and assumptions used in calculation of fair value
Expected volatility (as a percent)	36.00%	44.00%	35.00%	47.00%
Risk-free interest rate (as a percent)	0.09%	0.12%	0.09%	0.13%
Expected life	6 months	6 months	6 months	6 months
Weighted-average grant date fair value (in dollars per share)	$ 7.55	$ 7.68	$ 7.84	$ 7.59
Stock Options
Stock Option Grants
Common stock issued in connection with the exercise of stock options (in shares)	164,441	311,794	258,750	507,318
Weighted-average exercise price of common stock issued (in dollars per share)	$ 11.51	$ 17.04	$ 11.16	$ 16.70
Weighted-average fair values and assumptions used in calculation of fair value
Expected volatility (as a percent)	44.00%	45.00%	44.00%	46.00%
Risk-free interest rate (as a percent)	1.91%	1.46%	1.97%	1.29%
Expected life	6 years 3 months 29 days	6 years 7 months 28 days	6 years 7 months 10 days	6 years 7 months 24 days
Weighted-average grant date fair value (in dollars per share)	$ 12.63	$ 16.71	$ 14.13	$ 13.73
Employee Stock Options
Stock Option Grants
Options granted to purchase shares of common stock to employees (in shares)	70,000	57,750	442,010	375,250
Restricted Stock Units \| Service-Based Vesting
Stock awards other than options
Stock awards (in shares)	13,934	15,760	345,187	268,523
Grant-date fair value (in dollars)	370,226	441,000	10,100,000	7,700,000
Number of shares of common stock to be received for each restricted stock unit			1
Shares of common stock issued in connection with the vesting of the stock award	8,141	9,508	172,673	211,463
Weighted-average fair value (in dollars per share)	$ 31.95	$ 32.05	$ 28.17	$ 26.69
Restricted Stock Units \| Performance-Based Vesting
Stock awards other than options
Stock outstanding (in shares)	40,600		40,600
Grant-date fair value (in dollars)			1,100,000
Number of performance milestones on which vesting of awards is based			3
Employee Stock-Based Compensation Expense
Stock-based compensation expense (in dollars)	0		0
Restricted Stock Units \| Performance-Based Vesting \| Maximum
Stock awards other than options
Vesting percentage			100.00%
Restricted Stock Units \| Vesting on achievement of revenue milestone \| Minimum
Stock awards other than options
Vesting percentage			0.00%
Restricted Stock Units \| Vesting on achievement of revenue milestone \| Maximum
Stock awards other than options
Vesting percentage			100.00%
Restricted Stock Units \| Vesting on achievement of tests delivered milestone \| Minimum
Stock awards other than options
Vesting percentage			0.00%
Restricted Stock Units \| Vesting on achievement of tests delivered milestone \| Maximum
Stock awards other than options
Vesting percentage			100.00%
Restricted Stock Units \| Vesting on achievement of reimbursement-related milestone \| Minimum
Stock awards other than options
Vesting percentage			0.00%
Restricted Stock Units \| Vesting on achievement of reimbursement-related milestone \| Maximum
Stock awards other than options
Vesting percentage			33.33%
Restricted Stock Units \| Employees \| Annual vesting over vesting period
Stock awards other than options
Vesting percentage			33.00%
Vesting period			3 years
Restricted Stock \| Outside directors
Stock awards other than options
Stock awards (in shares)	2,256	2,142	3,961	3,977
Grant-date fair value (in dollars)	$ 60,000	$ 60,000	$ 110,000	$ 110,000
Weighted-average fair value (in dollars per share)	$ 26.57	$ 27.99	$ 27.73	$ 27.64