Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands				12 Months Ended
		Jan. 01, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	[2]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 3,841,951		$ 4,423,974	$ 3,841,951	$ 3,427,741
Cumulative effect of change in accounting principle related to marketable equity securities		(160)	[1]				$ 10,510
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[3]	0
Net unrealized gains (losses) arising during the period				42,534	(12,598)	15,284
Amount reclassified from AOCI				(2,768)	(1,786)	(4,657)
Other comprehensive income (loss)				39,766	(14,384)	10,627
Ending balance				5,017,617	4,423,974	3,841,951
Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(30,898)		(45,821)	(30,898)	(28,772)
Net unrealized gains (losses) arising during the period				46,170	(6,866)	2,531
Amount reclassified from AOCI				(2,768)	(1,786)	(4,657)
Other comprehensive income (loss)				43,402	(8,652)	(2,126)
Ending balance				(2,419)	(45,821)	(30,898)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(6,621)		(12,353)	(6,621)	(19,374)
Net unrealized gains (losses) arising during the period				(3,636)	(5,732)	12,753
Amount reclassified from AOCI				0	0	0
Other comprehensive income (loss)				(3,636)	(5,732)	12,753
Ending balance				(15,989)	(12,353)	(6,621)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(37,519)		(58,174)	(37,519)	(48,146)
Cumulative effect of change in accounting principle related to marketable equity securities	[1]	385
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[3]	6,656
Other comprehensive income (loss)				39,766	(14,384)	10,627
Ending balance				$ (18,408)	$ (58,174)	$ (37,519)
Accounting Standards Update 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of change in accounting principle related to marketable equity securities		385
Accounting Standards Update 2016-01 | Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of change in accounting principle related to marketable equity securities		385
Accounting Standards Update 2016-01 | Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of change in accounting principle related to marketable equity securities		0
Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		(6,656)
Accounting Standards Update 2018-02 | Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		(6,656)
Accounting Standards Update 2018-02 | Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		0
Accounting Standards Update 2018-02 | Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		6,656
Scenario, Adjustment | Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(37,169)
Scenario, Adjustment | Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(6,621)
Scenario, Adjustment | Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		$ (43,790)

[1] Represents the impact of the adoption of Accounting Standards Update (“ASU”) 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities in the first quarter of 2018. Refer to Note 1 — Summary of Significant Accounting Policies to the Consolidated Financial Statements in this Annual Report on Form 10-K (“this Form 10-K”) for additional information.

[2] Represents the impact of the adoption of ASU 2016-02, Leases (Topic 842) and subsequent related ASUs in the first quarter of 2019. Refer to Note 1 — Summary of Significant Accounting Policies and Note 10 — Leases to the Consolidated Financial Statements in this Form 10-K for additional information.

[3] Represents amounts reclassified from AOCI to retained earnings due to the early adoption of ASU 2018-02, Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income in the first quarter of 2018. Refer to Note 1 — Summary of Significant Accounting Policies to the Consolidated Financial Statements for additional information.