Share-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock option activity
Options outstanding (in shares)			202,215
Options exercised (in shares)			(69,965)
Options cancelled (in shares)			(1,380)
Options outstanding (in shares)	130,870		130,870
Options vested or expected to vest (in shares)	130,850		130,850
Options exercisable (in shares)	130,670		130,670
Stock option activity, weighted average exercise price
Options Outstanding, weighted average exercise price (in dollars per share)			$ 6.87
Options exercised, weighted average exercise price (in dollars per share)			6.75
Options canceled, weighted average exercise price (in dollars per share)			8.02
Options Outstanding, weighted average exercise price (in dollars per share)	$ 6.92		6.92
Options vested or expected to vest, weighted average exercise price (in dollars per share)	6.92		6.92
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.92		$ 6.92
Options outstanding, weighted average remaining contractual term			3 years 10 months 1 day
Options vested or expected to vest, weighted average remaining contractual term			3 years 10 months 1 day
Options exercisable, weighted average remaining contractual term			3 years 10 months 1 day
Options outstanding, aggregate intrinsic value	$ 2,012		$ 2,012
Options vested or expected to vest, aggregate intrinsic value	2,012		2,012
Options exercisable, aggregate intrinsic value	2,010		2,010
Intrinsic value of options exercised	13	$ 71	964	$ 197
Cash received from options exercised	7	48	473	208
Excess tax benefit realized for options exercises	$ 0	$ 10	$ 104	$ 19