Summary of Significant Accounting Policies - Comprehensive Income (Loss) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss consists of foreign currency translation adjustments, net of tax	$ 38,027,000	$ 37,486,000
Net unrealized losses on available-for-sale investments, net of tax	2,023,000	1,744,000
Losses on currency swaps, net of gains on long-term intercompany loans	1,271,000	1,271,000
Net realized gains reclassified into current operations	1,452,000	501,000	$ 829,000
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized gains reclassified into current operations	$ 1,452,000	$ 501,000	$ 829,000