Summary of Significant Accounting Policies (Accounting Standards Updates) (Details 3) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Retained Earnings	$ 1,551,900,000	$ 1,512,218,000
Accounting Standards Update 2018-02
Reclassification from AOCI	7,500,000
Retained Earnings	7,500,000
Income tax effects allocated to equity	$ 0