Consolidated Statements of Comprehensive Income Parenthetical - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Provision for (benefit from) income taxes	$ 0	$ 0	$ 500,000
(Provision for) benefit from income taxes	$ 0	$ 0	$ (500,000)