Fair Value Measurements - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Assets fair value	$ 231,049	$ 274,109
Liabilities:
Liabilities fair value	572	1,639
Restricted Cash
Assets:
Assets fair value	112,674
Certificates of Deposit
Assets:
Assets fair value	21,073	19,873
Certificates of Deposit—Restricted Cash
Assets:
Assets fair value	1,006	1,019
Money Market Mutual Funds
Assets:
Assets fair value	96,296	252,963
Foreign Currency Forward Contracts | Derivative Financial Instruments, Assets
Assets:
Assets fair value		254
Foreign Currency Forward Contracts | Derivative Financial Instruments, Liabilities
Liabilities:
Liabilities fair value	51	252
SARs | Share Based Compensation Liability
Liabilities:
Liabilities fair value	521	1,387
Level 1
Assets:
Assets fair value	208,970	252,963
Level 1 | Restricted Cash
Assets:
Assets fair value	112,674
Level 1 | Money Market Mutual Funds
Assets:
Assets fair value	96,296	252,963
Level 2
Assets:
Assets fair value	22,079	21,146
Liabilities:
Liabilities fair value	51	252
Level 2 | Certificates of Deposit
Assets:
Assets fair value	21,073	19,873
Level 2 | Certificates of Deposit—Restricted Cash
Assets:
Assets fair value	1,006	1,019
Level 2 | Foreign Currency Forward Contracts | Derivative Financial Instruments, Assets
Assets:
Assets fair value		254
Level 2 | Foreign Currency Forward Contracts | Derivative Financial Instruments, Liabilities
Liabilities:
Liabilities fair value	51	252
Level 3
Liabilities:
Liabilities fair value	521	1,387
Level 3 | SARs | Share Based Compensation Liability
Liabilities:
Liabilities fair value	$ 521	$ 1,387