Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Unaudited Consolidated Statements of Cash Flows [Abstract]
Net cash provided by operating activities	$ 32,397	$ 30,806
Investing activities:
Purchases of available-for-sale investments	(310,398)	(275,591)
Proceeds from sales or maturities of available-for-sale investments	286,580	262,707
Net sales of short-term investments	720	746
Other investing activities	(3,978)	(1,281)
Net cash used in investing activities	(27,076)	(13,419)
Financing activities:
Dividends paid to shareholders	(11,885)	(11,267)
Net cash used in financing activities	(11,885)	(11,267)
Effect of foreign exchange rates on cash and cash equivalents	398	(1,102)
Increase (decrease) in cash and cash equivalents	(6,166)	5,018
Cash and cash equivalents at beginning of period	73,538	64,632
Cash and cash equivalents at end of period	$ 67,372	$ 69,650