Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands				3 Months Ended
		Jan. 01, 2018		Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	[2]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 3,841,951		$ 4,423,974	$ 3,841,951
Cumulative effect of a change in accounting principle		(160)	[1]			$ 14,668
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[3]				0
Other comprehensive income (loss)				25,191	(12,014)
Ending balance				4,591,930	3,978,755
Available- for-Sale Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(30,898)		(45,821)	(30,898)
Net unrealized (losses) gains arising during the period				23,111	(17,311)
Amounts reclassified from AOCI				(1,100)	(1,501)
Other comprehensive income (loss)				22,011	(18,812)
Ending balance				(23,810)	(55,981)
Available- for-Sale Investment Securities | ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of a change in accounting principle		385
Available- for-Sale Investment Securities | ASU 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)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(6,621)		(12,353)	(6,621)
Net unrealized (losses) gains arising during the period				3,180	6,798
Amounts reclassified from AOCI				0	0
Other comprehensive income (loss)				3,180	6,798
Ending balance				(9,173)	177
Foreign Currency Translation Adjustments | ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of a change in accounting principle		0
Foreign Currency Translation Adjustments | ASU 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		0
AOCI, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(37,519)		(58,174)	(37,519)
Cumulative effect of a change in accounting principle		385	[1]			$ 0
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[3]				(6,656)
Net unrealized (losses) gains arising during the period				26,291	(10,513)
Amounts reclassified from AOCI				(1,100)	(1,501)
Other comprehensive income (loss)				25,191	(12,014)
Ending balance				$ (32,983)	$ (55,804)
AOCI, Net of Tax | ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of a change in accounting principle		385
AOCI, Net of Tax | ASU 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)
Scenario, Adjustment | Available- for-Sale 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 | AOCI, Net of Tax
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.

[2] Represents the impact of the adoption of ASU 2016-02, Leases (Topic 842) and subsequent ASUs in the first quarter of 2019. Refer to Note 2 — Current Accounting Developments and Note 11 — Leases to the Consolidated Financial Statements in this Form 10-Q 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.