Summary of Significant Accounting Policies - Pension and Other Postretirement Benefits (Details)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Investment gains and losses recognized, time period (years)	15 years
Other actuarial gains and losses recognized, time period (years)	10 years
Difference between fair value and expected market related value of plan assets (percent)	20.00%