Share-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock option activity
Options outstanding (in shares)			202,215
Options exercised (in shares)			(68,965)
Options cancelled (in shares)			(1,380)
Options outstanding (in shares)	131,870		131,870
Options vested or expected to vest (in shares)	131,070		131,070
Options exercisable (in shares)	118,140		118,140
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)	6.91		6.91
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.79		$ 6.79
Options outstanding, weighted average remaining contractual term			3 years 12 months 24 days
Options vested or expected to vest, weighted average remaining contractual term			3 years 11 months 5 days
Options exercisable, weighted average remaining contractual term			3 years 12 months 22 days
Options outstanding, aggregate intrinsic value	$ 2,010		$ 2,010
Options vested or expected to vest, aggregate intrinsic value	1,998		1,998
Options exercisable, aggregate intrinsic value	1,816		1,816
Intrinsic value of options exercised			951	$ 126
Cash received from options exercised			466	161
Excess tax benefit realized for options exercises	$ 10	$ 3	$ 104	$ 8