Share-Based Compensation - Stock Option Activity under Stock Option Plans (Details)	9 Months Ended	33 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	260,211
Granted (in shares) | shares		0
Exercised (in shares) | shares	(101,759)
Cancelled (in shares) | shares
Ending balance (in shares) | shares	158,452	158,452
Vested and Expected to Vest (in shares) | shares	158,452	158,452
Exercisable (in shares) | shares	158,452	158,452
Weighted-Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 19.26
Granted (in dollars per share) | $ / shares
Exercised (in dollars per share) | $ / shares	22.83
Cancelled (in dollars per share) | $ / shares
Ending balance (in dollars per share) | $ / shares	16.96	$ 16.96
Vested and Expected to Vest (in dollars per share) | $ / shares	16.96	16.96
Exercisable (in dollars per share) | $ / shares	$ 16.96	$ 16.96
Weighted Average Remaining Contractual Term (in Years)
Outstanding (term)	2 years 6 months 20 days
Vested and Expected to Vest (term)	2 years 6 months 20 days
Exercisable (term)	2 years 6 months 20 days
Aggregate Intrinsic Value
Outstanding | $	$ 4,114,422	$ 4,114,422
Vested and Expected to Vest | $	4,114,422	4,114,422
Exercisable | $	$ 4,114,422	$ 4,114,422