Investments Realized Gains and Losses from Sales of AFS Investments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2018	Jan. 01, 2017
Gain (Loss) on Securities [Line Items]
Proceeds from sales		$ 0	$ 19,673	$ 0	$ 35,550
Realized gains		0	0	0	7
Realized losses		0	0	0	(1)
Change in unrealized gain/ (loss) on equity securities reflected in the consolidated statement of operations		$ 0	$ 7	$ 0	$ (23)
Retained Earnings
Gain (Loss) on Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption	[1]						$ 334
Retained Earnings | ASU 2016-01
Gain (Loss) on Securities [Line Items]
Cumulative effect of new accounting principle in period of adoption						$ 339

[1] Reclassification due to the adoption of ASU 2016-01 and ASU 2017-12. See Part I. Item 1. “Financial Statements and Supplementary Data - Note 15: Recent Accounting Pronouncements.”