Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Money market and mutual funds	$ 128,563	$ 162,906
Derivative financial instruments	5,915	18,298
Total	134,478	181,204
Liabilities
Derivative financial instruments	10,178	877
Fair value of earn-out consideration		920
Total	10,178	1,797
Level 1
Assets
Money market and mutual funds	128,563	162,906
Derivative financial instruments	0	0
Total	128,563	162,906
Liabilities
Derivative financial instruments	0	0
Fair value of earn-out consideration		0
Total	0	0
Level 2
Assets
Money market and mutual funds	0	0
Derivative financial instruments	5,915	18,298
Total	5,915	18,298
Liabilities
Derivative financial instruments	10,178	877
Fair value of earn-out consideration		0
Total	10,178	877
Level 3
Assets
Money market and mutual funds	0	0
Derivative financial instruments	0	0
Total	0	0
Liabilities
Derivative financial instruments	0	0
Fair value of earn-out consideration		920
Total	$ 0	$ 920