Stockholder Rights Plan (Details)	12 Months Ended
	Dec. 31, 2017	Feb. 11, 2015	May 09, 2013
Equity [Abstract]
Period of cumulative change in ownership	3 years
Aggregate increase in common stock owned	50.00%
Ownership interest to cause cumulative change in ownership (or more than) (as a percent)	5.00%
Beneficial owner of common stock percentage (or more than)		4.90%	4.90%
Triggering threshold for rights issued pursuant to the plan	15.00%
Period of review	3 years
Beneficial ownership percentage post standstill period (up to)	50.00%
Beneficial owner of common stock percentage in future (more than)	50.00%
Period of offer to purchase common stock	60 days