Schedule II - Valuation and Qualifying Accounts (Parenthetical) (Details) - Allowance for Doubtful Accounts - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Uncollectible accounts written off		$ 900,000	$ 200,000
Uncollectible accounts recoveries	$ 0