Stockholders' Equity - Stock Option Activity (Details) - Equity Incentive Plan $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Options Outstanding
Outstanding, beginning of period (In shares) | shares	659,334
Options exercised (In shares) | shares	(105,610)
Outstanding, end of period (In shares) | shares	553,724
Exercisable (In shares) | shares	429,270
Weighted Average Exercise Price
Outstanding, beginning of period (In dollars per share) | $ / shares	$ 8.12
Options exercised (In dollars per share) | $ / shares	9.93
Outstanding, end of period (In dollars per share) | $ / shares	7.77
Exercisable (In dollars per share) | $ / shares	$ 7.66
Additional Disclosures
Outstanding, weighted average remaining contractual life	4 years 21 days
Exercisable, weighted average remaining contractual life	4 years 14 days
Outstanding, aggregate intrinsic value | $	$ 3,253,558
Exercisable, aggregate intrinsic value | $	$ 2,572,312