Summary of Significant Accounting Policies - Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss consists of foreign currency translation adjustments, net of tax	$ 38,030,000	$ 28,630,000
Net unrealized losses on available-for-sale investments, net of tax	130,000	36,000
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	673,000	314,000	1,695,000
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized gains reclassified into current operations	673,000	314,000	1,695,000
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized gains on derivative instruments	$ (32,000)	$ (104,000)	$ 0