Fair Value Measurements (Policies)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Determination of when transfers between fair value levels occurs	In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, the investments', non-financial assets' and/or liabilities' level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and consideration of factors specific to the investment. Significant transfers, if any, between the levels within the fair value hierarchy are recognized at the beginning of the reporting period when changes in circumstances require such transfers.