Equity Method Investments - Activity Related to Equity Method Investments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity Method Investments
Balance at beginning of period			$ 86,077	$ 129,524
Contributions			62,905	13,626
Loss on equity method investments	$ (4)	$ (1,286)	(998)	(2,569)
Balance at end of period	$ 147,984	140,581	$ 147,984	140,581
Constitution
Schedule of Equity Method Investments [Line Items]
Ownership percentage	25.00%		25.00%
Equity Method Investments
Balance at beginning of period			$ 732	96,850
Contributions			250	3,125
Loss on equity method investments			(982)	(2,555)
Balance at end of period	$ 0	97,420	0	97,420
Basis difference in investment	$ 95,900		$ 95,900
Meade
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%		20.00%
Equity Method Investments
Balance at beginning of period			$ 85,345	32,674
Contributions			62,655	10,501
Loss on equity method investments			(16)	(14)
Balance at end of period	$ 147,984	$ 43,161	147,984	$ 43,161
Investment Commitment
Equity Method Investments
Expected future contributions	$ 70,000		$ 70,000

Equity Method Investments [Roll Forward]

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- Definition

Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Amount of other commitments maturing in the remainder of the fiscal year following the latest fiscal year ended.

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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