Organization and Significant Accounting Policies, Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance		$ 365,280	$ 39,613	$ 200,790
Net other comprehensive loss for the period		(257)	(1,401)	(16,793)
Balance		1,187,160	365,280	39,613
Income tax expense included in other comprehensive loss		300	0	0
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance		(31,759)	(30,358)	(13,565)
Balance		(32,016)	(31,759)	(30,358)
Unrealized Losses on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive loss before reclassifications, net of tax	[1]	(280)	(960)	(17,219)
Amounts reclassified from accumulated other comprehensive loss		0	(374)	447
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive loss before reclassifications, net of tax		$ 23	$ (67)	$ (21)

[1] A tax benefit of $0.3 million was included in other comprehensive loss for the year ended December 31, 2018. There was no tax benefit or expense for other comprehensive loss for the years ended December 31, 2017 or 2016.