Plan Information (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) shares
Incentive compensation plan initiation year	2014
Number of shares initially available for grant	28.8
Maximum shares participants are eligible to receive	2.0
Maximum cash award per employee | $	$ 10.0
Number of years stock options expire from grant date	10 years
Vesting period in which the fair value of shares on grant date is amortized over, years	3 years
Minimum [Member]
Stock options exercisable period	2 years
Maximum [Member]
Stock options exercisable period	4 years