Recently Issued Accounting Standards - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Description of timing of performance obligation			The fixed portion of the transaction price will be recognized over the primary term of the contract, which is generally five years. The timing of the payment of the fixed portion of the transaction price is upfront, however, the performance obligation is satisfied over the primary term of the contract, which is generally five years. This revenue consists of up-front lease bonus payments received under royalty contracts that are recognized over the primary term of the royalty agreement, which is generally five years.
Revenue recognized in contract liability		$ 400	$ 1,000
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract liability	$ 2,600
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings	2,300
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings			$ 2,339
Retained Earnings | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle	2,075
Cumulative effect of new accounting principle, net of tax	500
Retained Earnings | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle	$ (2,727)