Shareholders' Equity, Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 404,345	$ 394,498
Other comprehensive income (loss)	$ 2,679	$ 2,591	11,947	(1,116)
Ending balance	404,930	406,922	404,930	406,922
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			33,220	37,858
Other comprehensive income before reclassifications			16,509	7,869
Amounts reclassified from accumulated other comprehensive income			(4,562)	(8,985)
Other comprehensive income (loss)			11,947	(1,116)
Ending balance	45,167	36,742	45,167	36,742
Foreign Currency [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(831)	(1,066)
Other comprehensive income before reclassifications			510	398
Amounts reclassified from accumulated other comprehensive income			0	0
Other comprehensive income (loss)			510	398
Ending balance	(321)	(668)	(321)	(668)
Unrealized Holding Gains on Available-for-sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			34,051	38,924
Other comprehensive income before reclassifications			15,999	7,471
Amounts reclassified from accumulated other comprehensive income			(4,562)	(8,985)
Other comprehensive income (loss)			11,437	(1,514)
Ending balance	$ 45,488	$ 37,410	$ 45,488	$ 37,410