Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands			12 Months Ended
		Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 3,841,951	$ 3,841,951	$ 3,427,741	$ 3,122,950
Cumulative effect of change in accounting principle related to marketable equity securities	[1]	(160)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[2]	0
Other comprehensive (loss) income			(14,384)	10,627	(33,205)
Ending balance			4,423,974	3,841,951	3,427,741
Available- for-Sale Debt and Equity Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(30,898)	(30,898)	(28,772)	(6,144)
Net unrealized gains (losses) arising during the period				2,531	(16,623)
Amount reclassified from AOCI				(4,657)	(6,005)
Other comprehensive (loss) income				(2,126)	(22,628)
Ending balance				(30,898)	(28,772)
Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Net unrealized gains (losses) arising during the period			(6,866)
Amount reclassified from AOCI			(1,786)
Other comprehensive (loss) income			(8,652)
Ending balance			(45,821)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(6,621)	(6,621)	(19,374)	(8,797)
Net unrealized gains (losses) arising during the period			(5,732)	12,753	(10,577)
Amount reclassified from AOCI			0	0	0
Other comprehensive (loss) income			(5,732)	12,753	(10,577)
Ending balance			(12,353)	(6,621)	(19,374)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(37,519)	(37,519)	(48,146)	(14,941)
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	[2]	(6,656)
Net unrealized gains (losses) arising during the period			(12,598)	15,284	(27,200)
Amount reclassified from AOCI			(1,786)	(4,657)	(6,005)
Other comprehensive (loss) income			(14,384)	10,627	(33,205)
Ending balance			$ (58,174)	$ (37,519)	$ (48,146)
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 2016-01 | Total
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 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 [Member] | Available- for-Sale Debt Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(37,169)
Scenario, Adjustment [Member] | Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(6,621)
Scenario, Adjustment [Member] | 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 for additional information.

[2] 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.