Balance Sheet Parenthetical (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale Debt Securities, Amortized Cost Basis	$ 3,594,591	$ 3,426,217
Available-for-sale Equity Securities, Amortized Cost Basis		163,106
Securities Received as Collateral	$ 39,077	$ 19,357
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Common Stock, Shares Authorized	485,000,000	485,000,000
Common Stock, Shares, Issued	233,160,146	233,416,989
Common Stock, Shares, Outstanding	215,542,607	215,814,188
Treasury Stock, Shares	17,617,539	17,602,801