Investments Proceeds from Sale and Gains and Losses on Held-to-Maturity Securities (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Debt Securities, Held-to-maturity, Sale, Excluding Other-than-temporary Impairment [Abstract]
Proceeds from sale of held-to-maturity securities	[1]	$ 161,743	$ 0
Amortized cost of held-to-maturity securities	[1]	121,010	0
Realized net gain from sale of held-to-maturity securities	[1]	$ 40,733	$ 0

[1] The securities sold had less than 15 percent of the acquired principal outstanding at the time of the sale. Such sales are treated as maturities for the purposes of security classification. The sale does not impact our ability and intent to hold the remaining investments classified as held-to-maturity through their stated maturity dates.