Stock-Based Compensation (Detail) (USD $)	3 Months Ended		12 Months Ended	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	7,070,000
Common stock par value (in Dollars per share)	$ 0.0005		0.0005
Total share-based compensation cost not yet recognized	$ 74,500,000
Total compensation cost not yet recognized, period for recognition	2 years 8 months 12 days
Stock appreciation rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Award expiration period from date of grant	7 years
Total compensation cost not yet recognized, period for recognition	4 years
Outstanding shares unvested	1,700,000	[1],[2]	1,400,000
Aggregate Intrinsic value of outstanding shares	52,500,000
Aggregate intrinsic value of shares vested and exercisable	38,100,000
Stock grants during period	300,000
Weighted average remaining contractual terms	4 years 5 months 82 days	[1],[2]	4 years 4 months 2 days
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Outstanding shares unvested	1,400,000	[3],[4]	1,400,000
Stock grants during period	600,000	[5]
Weighted average remaining contractual terms	1 year 9 months 3 days
Restricted stock units (RSUs) | Executive officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock grants during period	400,000
Restricted stock units (RSUs) | Non executive
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock grants during period	200,000
Performance-based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Common stock equivalents (CSEs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding shares unvested	104,589		104,203
Stock grants during period	1,900
Base fee percentage	50.00%
Target amount | Restricted stock units (RSUs) | Executive officer | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares authorized for grant	0.00%
Target amount | Restricted stock units (RSUs) | Executive officer | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares authorized for grant	200.00%
Unvested | Stock appreciation rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding shares unvested	800,000
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan, stock purchases as percentage of employee compensation maximum	10.00%
Maximum share value authorized for purchase under employee stock purchase plan	23,750
Exercisable price percentage of closing price of another class of stock	95.00%
Maximum number of shares that may be purchased by eligible participants	1,100,000
Proceeds from stock plans	$ 2,100,000			$ 1,500,000

[1] Total SARs outstanding had an intrinsic value of $52.5 million. SARs vested and exercisable had an intrinsic value of $38.1 million.

[2] As of March 31, 2015, 0.8 million of the SARs outstanding were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.

[3] The weighted-average remaining contractual term of the outstanding RSUs is approximately 1.8 years.

[4] The Company expects that substantially all of the outstanding awards will vest in future periods.

[5] The 0.6 million RSUs granted consisted of 0.4 million performance-based RSUs awarded to executives and 0.2 million service-based RSUs awarded to non-executive employees and non-management board members. The 0.4 million performance-based RSUs represents the target amount of the grant for the year, which is tied to an increase in the Company’s subscription-based research contract value (“CV”) for 2015. The final number of performance-based RSUs that will ultimately be awarded for 2015 ranges from 0% to 200% of the target amount, with the final number dependent on the actual increase in CV for 2015 as measured on December 31, 2015. If the specified minimum level of achievement is not met, the performance-based RSUs will be forfeited in their entirety, and any compensation expense previously recorded will be reversed.