Stock Based Compensation - Schedule of Stock Options Exercise Price (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Class of Stock [Line Items]
Exercise price, options outstanding (in shares)	7,616
Exercise price, options exercisable (in shares)	5,174
$10.00 – $40.65
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 10.00
Exercise price, maximum (in usd per share) | $ / shares	$ 40.65
Exercise price, options outstanding (in shares)	1,874
Exercise price, weighted average remaining vesting life in years	1 day
Exercise price, options exercisable (in shares)	1,874
87.61 – 138.47
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 87.61
Exercise price, maximum (in usd per share) | $ / shares	$ 138.47
Exercise price, options outstanding (in shares)	1,868
Exercise price, weighted average remaining vesting life in years	2 months 5 days
Exercise price, options exercisable (in shares)	1,428
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)	2,534
Exercise price, weighted average remaining vesting life in years	11 months 1 day
Exercise price, options exercisable (in shares)	1,430
151.16 – 156.04
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 151.16
Exercise price, maximum (in usd per share) | $ / shares	$ 156.04
Exercise price, options outstanding (in shares)	519
Exercise price, weighted average remaining vesting life in years	8 months 16 days
Exercise price, options exercisable (in shares)	326
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)	424
Exercise price, weighted average remaining vesting life in years	2 years 1 month 10 days
Exercise price, options exercisable (in shares)	108
199.75 – 206.73
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 199.75
Exercise price, maximum (in usd per share) | $ / shares	$ 206.73
Exercise price, options outstanding (in shares)	289
Exercise price, weighted average remaining vesting life in years	3 years 5 days
Exercise price, options exercisable (in shares)	0
209.05 – 216.18
Class of Stock [Line Items]
Exercise price, minimum (in usd per share) | $ / shares	$ 209.05
Exercise price, maximum (in usd per share) | $ / shares	$ 216.18
Exercise price, options outstanding (in shares)	108
Exercise price, weighted average remaining vesting life in years	2 years 11 months 19 days
Exercise price, options exercisable (in shares)	8