Shareholders' Equity, Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 418,811	$ 404,345
Other comprehensive income (loss) before reclassifications	(3,221)	6,055
Amounts reclassified from accumulated other comprehensive income (loss)	(123)	(655)
Other comprehensive income (loss)	(3,344)	5,400
Ending balance	411,811	412,902
ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption	(46,157)
ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption	117
Other Comprehensive Income (Loss) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	46,391	33,220
Ending balance	(2,993)	38,620
Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	234
Cumulative effect of adoption			$ 46,157
Other Comprehensive Income (Loss) [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption	117
Foreign Currency [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(309)	(831)
Other comprehensive income (loss) before reclassifications	(223)	65
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive income (loss)	(223)	65
Ending balance	(532)	(766)
Foreign Currency [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(309)
Cumulative effect of adoption	0
Foreign Currency [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption	0
Unrealized Holding Gains on Available-for-sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	46,700	34,051
Other comprehensive income (loss) before reclassifications	(2,998)	5,990
Amounts reclassified from accumulated other comprehensive income (loss)	(123)	(655)
Other comprehensive income (loss)	(3,121)	5,335
Ending balance	(2,461)	$ 39,386
Unrealized Holding Gains on Available-for-sale Securities [Member] | ASU 2016-01 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	543
Cumulative effect of adoption	(46,157)
Unrealized Holding Gains on Available-for-sale Securities [Member] | ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of adoption	$ 117