Business Information - Information by Geographic Region, After Elimination of All Significant Inter-company Accounts and Transactions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 101,600	$ 76,600	$ 90,500	$ 66,900	$ 75,700	$ 50,600	$ 73,300	$ 61,900	$ 335,519	$ 261,560	$ 275,234
Income (loss) before taxes	32,400	$ 19,200	$ 29,900	$ 6,500	14,200	$ 1,100	$ 15,700	$ 12,200	87,881	43,295	67,470
Total assets	456,682				423,144				456,682	423,144	336,956
North America
Segment Reporting Information [Line Items]
Total revenues									206,673	172,582	160,631
Income (loss) before taxes									48,927	40,895	36,745
Total assets	266,975				261,077				266,975	261,077	165,204
Europe
Segment Reporting Information [Line Items]
Total revenues									110,229	63,875	83,369
Income (loss) before taxes									52,650	9,577	24,891
Total assets	64,467				38,409				64,467	38,409	33,460
Rest of World
Segment Reporting Information [Line Items]
Total revenues									18,617	25,103	31,234
Income (loss) before taxes									(13,696)	(7,177)	5,834
Total assets	$ 125,240				$ 123,658				$ 125,240	$ 123,658	$ 138,292