Fair Value Measurement (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (1,235)	$ 51,115
Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	163	499
Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	26	60,477
Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(1,424)	(9,861)
Commercial paper
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		22,872
Commercial paper | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Commercial paper | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		22,872
Commercial paper | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Corporate bonds
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		28,060
Corporate bonds | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Corporate bonds | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		28,060
Corporate bonds | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Commodity contract derivatives
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	189	10,044
Commodity contract derivatives | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	163	499
Commodity contract derivatives | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	26	9,545
Commodity contract derivatives | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(1,424)	(9,861)
Contingent considerations for acquisitions | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent considerations for acquisitions | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (1,424)	$ (9,861)