Unrecognized cost of unvested share-based compensation awards.

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Stock-Based Compensation - Share Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding (in shares)	16,250
Exercised (in shares)	(5,750)
Forfeited or expired (in shares)	0
Outstanding (in shares)	10,500	16,250
Exercisable (in shares)	10,500
Vested (in shares)	10,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted-average exercise price (in dollars per share)	$ 8.37
Exercised, weighted-average exercise price (in dollars per share)	7.80
Forfeited or expired, weighted-average exercise price (in dollars per share)	0
Outstanding, weighted-average exercise price (in dollars per share)	8.68	$ 8.37
Exercisable, weighted-average exercise price (in dollars per share)	8.68
Vested, weighted-average exercise price (in dollars per share)	$ 8.68
Outstanding, average remaining contractual term (in years)	2 years 8 months 12 days	3 years 8 months 12 days
Exercisable, average remaining contractual term (in years)	2 years 8 months 12 days
Vested, average remaining contractual term	2 years 8 months 12 days
Outstanding, aggregate intrinsic value	$ 380,000	$ 804,000
Exercisable, aggregate intrinsic value	380,000
Vested, aggregate intrinsic value	380,000
Total intrinsic value of share options exercised	200,000	400,000	$ 200,000
Options, vested in period, fair value	$ 0	$ 0	$ 4,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Contractual term	10 years
Grants in period (in shares)	0	0	0
Expected volatility factor				46.25%
Expected dividend yield (percent)				0.00%
Expected term (in years)				6 years 3 months
Risk free interest rate (percent)				2.03%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Total compensation cost not yet recognized	$ 0	$ 0	$ 0