Current Accounting Developments Current Accounting Developments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Marketable equity securities			$ 31,900
Cumulative effect of a change in accounting principle	[1]		(160)
Private Equity Funds
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost method investments		$ 11,400
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of a change in accounting principle	[1]		(545)
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[2]	6,656
AOCI, Net of Tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of a change in accounting principle	[1]		385
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[2]	$ (6,656)
ASU 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of a change in accounting principle			(545)
ASU 2016-01 | AOCI, Net of Tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of a change in accounting principle			$ 385

[1] Represents the impact of the adoption in the first quarter of 2018 of Accounting Standards Update (“ASU”) 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. Refer to Note 2 — Current Accounting Developments 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 during the first quarter of 2018. Refer to Note 2 — Current Accounting Developments to the Consolidated Financial Statements for additional information.