Stock Based Compensation - Schedule of Stock Options Exercise Price (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Class of Stock [Line Items]
Exercise price, options outstanding (in shares)	8,031
Exercise price, options exercisable (in shares)	4,029
$10.00 – 58.02
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 10.00
Exercise price, maximum (in usd per share) | $ / shares	$ 58.02
Exercise price, options outstanding (in shares)	2,218
Exercise price, weighted average remaining vesting life in years	1 day
Exercise price, options exercisable (in shares)	2,218
74.99 – 111.09
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 74.99
Exercise price, maximum (in usd per share) | $ / shares	$ 111.09
Exercise price, options outstanding (in shares)	104
Exercise price, weighted average remaining vesting life in years	11 days
Exercise price, options exercisable (in shares)	90
114.90 – 138.47
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 114.9
Exercise price, maximum (in usd per share) | $ / shares	$ 138.47
Exercise price, options outstanding (in shares)	2,029
Exercise price, weighted average remaining vesting life in years	9 months 7 days
Exercise price, options exercisable (in shares)	577
140.23-150.74
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 140.23
Exercise price, maximum (in usd per share) | $ / shares	$ 150.74
Exercise price, options outstanding (in shares)	2,593
Exercise price, weighted average remaining vesting life in years	1 year 7 months 6 days
Exercise price, options exercisable (in shares)	906
151.16-158.24
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 151.16
Exercise price, maximum (in usd per share) | $ / shares	$ 158.24
Exercise price, options outstanding (in shares)	618
Exercise price, weighted average remaining vesting life in years	1 year 5 months 23 days
Exercise price, options exercisable (in shares)	195
165.96-174.35
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 165.96
Exercise price, maximum (in usd per share) | $ / shares	$ 174.35
Exercise price, options outstanding (in shares)	469
Exercise price, weighted average remaining vesting life in years	3 years 29 days
Exercise price, options exercisable (in shares)	43