Share Repurchase Program - Narrative (Details) - USD ($)		12 Months Ended
	Feb. 12, 2015	Dec. 31, 2017	Dec. 31, 2015	May 04, 2017
Equity [Abstract]
Authorized share repurchase	$ 20,000,000			$ 30,000,000
Term of share repurchase program	2 years
Acquisition of treasury shares (in shares)		1,121,928
Value of shares repurchased		$ 10,976,000	$ 4,897,000
Cost per share acquired (in USD per share)		$ 9.78