Fair Value of Financial Assets and Liabilities, Financial Impact of Qualifying Cash Flow Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss related to cash flow hedges at Jan. 1	$ (23,836)	$ (23,878)	$ (23,338)
After-tax net unrealized (losses) related to derivatives accounted for as hedges	0	(30)	(72)
After-tax net realized losses (gains) on derivative transactions reclassified into earnings	1,056	72	(468)
Accumulated other comprehensive loss related to cash flow hedges at Dec. 31	$ (22,780)	$ (23,836)	$ (23,878)