Stock Plans and Stock Based Compensation - Activity Related to Restricted Stock Awards (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of Shares
Unvested, January 1, 2017 (in shares) | shares	251,716
Granted (in shares) | shares	59,333
Vested (in shares) | shares	(44,073)
Forfeited (in shares) | shares	(5,603)
Unvested, December 31, 2017 (in shares) | shares	261,373
Weighted Average Fair Value
January 1, 2017 (in dollars per share) | $ / shares	$ 54.46
Granted (in dollars per share) | $ / shares	79.51
Vested (in dollars per share) | $ / shares	46.76
Forfeited (in dollars per share) | $ / shares	60.72
December 31, 2017 (in dollars per share) | $ / shares	$ 61.32