Share-Based Payments - Employee Stock Purchase Plan Narrative (Details) - Employee Stock Purchase Plan $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) hour $ / shares shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance (in shares)			1,024,652
Number of hours worked (in hours) | hour	20
Eligible purchase price of common stock under stock plan ( as a percent)	85.00%
Shares issued during period (in shares)	104,892
Shares issued under the plan (in shares)	742,366
Share available for grant (in shares)	282,286
Subscriptions outstanding (in shares)	64,138
Fair value of subscriptions outstanding (in dollars per share) | $ / shares	$ 3.61
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 4.32	$ 4.05	$ 4.51
Cash received under plan | $	$ 1.1	$ 1.0	$ 1.1
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction range on cash compensation (as a percent)	15.00%