Share-Based Compensation - Stock Option Activity under Stock Option Plans (Details)	6 Months Ended	30 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	260,211
Granted (in shares) | shares		0
Exercised (in shares) | shares	(92,054)
Cancelled (in shares) | shares
Ending balance (in shares) | shares	168,157	168,157
Vested and Expected to Vest (in shares) | shares	168,157	168,157
Exercisable (in shares) | shares	168,157	168,157
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	22.61
Cancelled (in dollars per share) | $ / shares
Ending balance (in dollars per share) | $ / shares	17.42	$ 17.42
Vested and Expected to Vest (in dollars per share) | $ / shares	17.42	17.42
Exercisable (in dollars per share) | $ / shares	$ 17.42	$ 17.42
Weighted Average Remaining Contractual Term (in Years)
Outstanding (term)	2 years 8 months 15 days
Vested and Expected to Vest (term)	2 years 8 months 15 days
Exercisable (term)	2 years 8 months 15 days
Aggregate Intrinsic Value
Outstanding | $	$ 3,820,566	$ 3,820,566
Vested and Expected to Vest | $	3,820,566	3,820,566
Exercisable | $	$ 3,820,566	$ 3,820,566