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	$ (54,862)	$ (57,628)	$ (59,753)
After-tax net unrealized gains (losses) related to derivatives accounted for as hedges	3	(70)	(163)
After-tax net realized losses on derivative transactions reclassified into earnings	3,708	2,836	2,288
Accumulated other comprehensive loss related to cash flow hedges at Dec. 31	$ (51,151)	$ (54,862)	$ (57,628)