Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity Attributable to Parent Beginning Balance			$ 2,894,582
Net Income Attributable to Parent	$ 50,240	$ 56,785	122,485	$ 132,203
OCI, Net of Tax, Portion Attributable to Parent			80,197	(10,374)
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options			22,050
Treasury Stock Purchases			(3,275)
Stockholders' Equity Attributable to Parent Ending Balance	3,116,483		3,116,483
Stockholders' Equity Attributable to Noncontrolling Interest Beginning Balance			292,539
Net income attributable to noncontrolling interest	3,145	0	6,317	0
OCI, Net of Tax, Portion Attributable to Noncontrolling Interest			18,346
Stockholders' Equity, Other			438
Stockholders' Equity Attributable to Noncontrolling Interest Ending Balance	317,196		317,196
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning Balance			3,187,121
Net income	53,385	56,785	128,802	132,203
Other Comprehensive Income, Net of Tax	33,676	$ 4,430	98,543	$ (10,374)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance	$ 3,433,679		3,433,679
Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options			22,050
Treasury Stock Purchases			3,275
Stockholders' Equity, Other			444
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other			$ (6)