Notes Payable - Banks (Details Textual) € in Thousands, $ in Thousands	1 Months Ended		6 Months Ended
	Dec. 18, 2014 USD ($)	Jun. 19, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 EUR (€)	Jun. 30, 2015 EUR (€)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 EUR (€)
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	$ 275,000	$ 200,000	$ 34,994			$ 36,586
Line of Credit Facility, Remaining Borrowing Capacity			25,000
Excess Capital	$ 50,000
Line of Credit Facility, Current Borrowing Capacity			214,594			229,386
Line of Credit Facility, Expiration Date	Jun. 19, 2017
Line of Credit Facility, Commitment Fee Amount			8,913	€ 8,000
Line of Credit Facility, Fair Value of Amount Outstanding			$ 5,236		€ 4,700	$ 8,288	€ 6,850
Line Of Credit Facility, Interest Rate, Variable Rate Basis			EURIBOR plus 1.75%	EURIBOR plus 1.75%
Committed Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding			$ 138,600
Line of Credit Facility, Maximum Borrowing Capacity	$ 185,000
Line of Credit Facility, Current Borrowing Capacity	35,000
Uncommitted Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding			$ 41,000
Line of Credit Facility, Maximum Borrowing Capacity	90,000
Line of Credit Facility, Current Borrowing Capacity	$ 15,000
Rabobank International [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding		300,000
Line of Credit Facility, Maximum Borrowing Capacity		150,000
Line of Credit Facility, Remaining Borrowing Capacity		75,000
Line of Credit Facility, Increase (Decrease), Other, Net		$ 75,000