Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent Beginning Balance			$ 2,894,582
Net Income Attributable to Parent	$ 46,007	$ 48,399	72,245	$ 75,418
OCI, Net of Tax, Portion Attributable to Parent			51,876	(14,804)
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options			11,267
Stockholders' Equity Attributable to Parent Ending Balance	3,029,895		3,029,895
Stockholders' Equity Attributable to Noncontrolling Interest Beginning Balance			292,539
Net Income Attributable to Noncontrolling Interest	2,121	0	3,172	0
OCI, Net of Tax, Portion Attributable to Noncontrolling Interest			12,991
Stockholders' Equity, Other			(102)
Stockholders' Equity Attributable to Noncontrolling Interest Ending Balance	308,675		308,675
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning Balance			3,187,121
Net income	48,128	48,399	75,417	75,418
Other Comprehensive Income, Net of Tax	29,001	$ (38,417)	64,867	$ (14,804)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance	$ 3,338,570		3,338,570
Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options			11,267
Stockholders' Equity, Other			(75)
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other			$ (27)