Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 1,357,283
Ending balance	1,347,312
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	2,247	$ 350
Other comprehensive income (loss)	607	(65)
Amount reclassified from Available-for-sale securities, net of tax	(2,956)
Ending balance	(102)	285
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	3,286	150
Other comprehensive income (loss)	170	68
Amount reclassified from Available-for-sale securities, net of tax	(2,956)
Ending balance	500	218
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,039)	200
Other comprehensive income (loss)	437	(133)
Amount reclassified from Available-for-sale securities, net of tax	0
Ending balance	$ (602)	$ 67