Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,782,485	$ 1,576,000	$ 1,407,287
Stockholders' Equity Attributable to Parent	1,782,485	1,576,000	1,576,000
Ending balance	2,119,912	1,782,485	1,576,000
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(34)	(67)	1,774
Stockholders' Equity Attributable to Parent	(34)	(34)	(67)
Ending balance		(34)	$ (67)
Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201802Member
Accounting Standards Update 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201601Member
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	0	$ 3,992
Adoption of ASU 2018-02	0	0	860
Stockholders' Equity Attributable to Parent	0	0	3,992
Ending balance	0	0	0
Accumulated Other Comprehensive Income | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(3,992)
Stockholders' Equity Attributable to Parent			(3,992)
Accumulated Other Comprehensive Income | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	0	(4,852)
Stockholders' Equity Attributable to Parent	$ 0	0	(4,852)
Ending balance		$ 0	$ 0