Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 1,444,098	$ 1,522,577	$ 1,509,537
Other comprehensive income (loss)	1,897	(1,475)	732
Reclassification of investment to trading security		(308)
Net current period other comprehensive income (loss)		(1,783)
Ending balance	1,357,283	1,444,098	1,522,577
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	350	2,133	1,401
Ending balance	2,247	350	2,133
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	150	352	36
Other comprehensive income (loss)	3,136	106	316
Reclassification of investment to trading security		(308)
Net current period other comprehensive income (loss)		(202)
Ending balance	3,286	150	352
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	200	1,781	1,365
Other comprehensive income (loss)	(1,239)	(1,581)	416
Reclassification of investment to trading security		0
Net current period other comprehensive income (loss)		(1,581)
Ending balance	$ (1,039)	$ 200	$ 1,781