Share-Based Compensation - Restricted Stock Units Activity (Details) - Restricted Stock	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares
Unvested, Beginning balance (in shares) | shares	182,023
Granted (in shares) | shares	28,555
Vested (in shares) | shares	(52,650)
Forfeited (in shares) | shares	(3,250)
Unvested, Ending balance (in shares) | shares	154,678
Weighted-Average Grant Date Fair Value
Unvested, Beginning balance (in dollars per share) | $ / shares	$ 83.37
Granted (in dollars per share) | $ / shares	138.06
Vested (in dollars per share) | $ / shares	78.82
Forfeited (in dollars per share) | $ / shares	84.78
Unvested, Ending balance (in dollars per share) | $ / shares	$ 94.98