Stock-Based Compensation - Summary of Changes in Number of Shares of Restricted Stock and Restricted Stock Units (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares
Shares outstanding, beginning of period (in shares) | shares	365
Granted (in shares) | shares	49
Vested (in shares) | shares	(47)
Canceled (in shares) | shares	(26)
Shares outstanding, end of period (in shares) | shares	341
Weighted Average Grant Date Fair Value
Weighted average grant date fair value, beginning of period (in dollars per share) | $ / shares	$ 155.58
Weighted average grant date fair value, granted (in dollars per share) | $ / shares	199.75
Weighted average grant date fair value, vested (in dollars per share) | $ / shares	158.54
Weighted average grant date fair value, canceled (in dollars per share) | $ / shares	154.46
Weighted average grant date fair value, end of period (in dollars per share) | $ / shares	$ 163.95