Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Unaudited Consolidated Statements of Cash Flows [Abstract]
Net cash provided by operating activities	$ 23,164	$ 22,741
Investing activities:
Purchases of available-for-sale investments	(231,601)	(215,228)
Proceeds from sales or maturities of available-for-sale investments	221,818	188,245
Net sales of short-term investments	0	720
Other investing activities	12,444	(1,112)
Net cash provided by (used in) investing activities	2,661	(27,375)
Financing activities:
Dividends paid to shareholders	(8,174)	(7,902)
Net cash used in financing activities	(8,174)	(7,902)
Effect of Foreign exchange rates on cash and cash equivalents	453	543
Increase (decrease) in cash and cash equivalents	18,104	(11,993)
Cash and cash equivalents at beginning of period	62,976	73,538
Cash and cash equivalents at end of period	$ 81,080	$ 61,545