Equity - AOCI Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in the balances of each component of AOCI
Balance at the beginning of the period	$ 840,093
Other comprehensive income (loss)	24	$ (99)
Balance at the end of the period	827,957
Accumulated Other Comprehensive Income
Changes in the balances of each component of AOCI
Balance at the beginning of the period	1,812
Other comprehensive income (loss)	24
Balance at the end of the period	1,836
Foreign Currency Translation
Changes in the balances of each component of AOCI
Balance at the beginning of the period	1,839
Other comprehensive income (loss)	32
Balance at the end of the period	1,871
Unrealized Gains (Losses) on Available for Sale Securities
Changes in the balances of each component of AOCI
Balance at the beginning of the period	(27)
Other comprehensive income (loss)	(8)
Balance at the end of the period	$ (35)