Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Number of Options
Outstanding at beginning of period (in shares) | shares	520
Granted (in shares) | shares	119
Exercised (in shares) | shares	(20)
Forfeited/canceled/expired (in shares) | shares	0
Outstanding at end of period (in shares) | shares	619
Vested and expected to vest at end of period (in shares) | shares	619
Exercisable at end of period (in shares) | shares	406
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 42.56
Granted (in dollars per share) | $ / shares	44.95
Exercised (in dollars per share) | $ / shares	21.95
Forfeited/canceled/expired (in dollars per share) | $ / shares	0.00
Outstanding at end of period (in dollars per share) | $ / shares	43.69
Vested and expected to vest at end of period (in dollars per share) | $ / shares	35.03
Exercisable at end of period (in dollars per share) | $ / shares	$ 39.82
Weighted-Average Remaining Contractual Term (in years)
Outstanding at end of period	4 years 8 months 9 days
Vested and expected to vest at end of period	3 years 4 months 10 days
Exercisable at end of period	3 years 10 months 10 days
Aggregate Intrinsic Value
Exercised | $	$ 464
Outstanding at end of period | $	7,151
Vested and expected to vest at end of period | $	6,304
Exercisable at end of period | $	$ 6,282