Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 404,345
Other comprehensive income before reclassifications			11,590
Amounts reclassified from accumulated other comprehensive income			(2,322)
Other comprehensive income (loss)	$ 3,868	$ 3,924	9,268	$ (3,707)
Ending balance	400,771		400,771
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			33,220
Ending balance	42,488		42,488
Foreign Currency [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(831)
Other comprehensive income before reclassifications			453
Amounts reclassified from accumulated other comprehensive income			0
Other comprehensive income (loss)			453
Ending balance	(378)		(378)
Unrealized Holding Gains on Available-for-sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			34,051
Other comprehensive income before reclassifications			11,137
Amounts reclassified from accumulated other comprehensive income			(2,322)
Other comprehensive income (loss)			8,815
Ending balance	$ 42,866		$ 42,866