Summary of Significant Accounting Policies - Comprehensive Income (Loss) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss consists of foreign currency translation adjustments, net of tax	$ 55,262,000	$ 49,646,000
Net unrealized losses on available-for-sale investments, net of tax	68,000	1,413,000
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	191,000	344,000	$ 673,000
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized gains reclassified into current operations	191,000	344,000	673,000
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gains on derivative instruments	$ (37,000)	$ (206,000)	$ (32,000)