Shareholders' Equity - AOCI Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			$ 1,330,043
Other comprehensive income	$ 126	$ 4,630	119	$ 20,023
Ending balance	1,239,361		1,239,361
Unrealized Gain on Investment in Equity Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0		45,116
Amounts reclassified from cumulative other comprehensive income to cumulative net income			(45,116)
Other comprehensive income before reclassifications	0		0
Amounts reclassified from cumulative other comprehensive loss to net income	0		0
Other comprehensive income	0		0
Ending balance	0		0
Equity in Unrealized Gain (Loss) of an Investee
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	139		15,311
Amounts reclassified from cumulative other comprehensive income to cumulative net income			(15,165)
Other comprehensive income before reclassifications	143		155
Amounts reclassified from cumulative other comprehensive loss to net income	(17)		(36)
Other comprehensive income	126		119
Ending balance	265		265
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	139		60,427
Amounts reclassified from cumulative other comprehensive income to cumulative net income			(60,281)
Other comprehensive income before reclassifications	143		155
Amounts reclassified from cumulative other comprehensive loss to net income	(17)		(36)
Other comprehensive income	126		119
Ending balance	$ 265		$ 265

Reclassification From AOCI To Retained Earnings, Current Period, Net Of Tax, Attributable To Parent

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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