Business Changes and Developments - Goodwill Associated with Acquisitions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Balance at beginning of period	$ 160,961	$ 166,461
Foreign Currency Translation and Other	8,819	(5,500)
Impairment of Goodwill	7,107
Sale of the Institutional Trust and Independent Fiduciary business of ETC	(28,442)
Balance at end of period	134,231	160,961	$ 166,461
Goodwill, Impaired, Accumulated Impairment Loss	35,607	28,500	28,500
Goodwill, Gross	169,838	189,461	194,961
Investment Banking [Member]
Goodwill [Roll Forward]
Balance at beginning of period	114,489	115,276
Foreign Currency Translation and Other	8,819	(787)
Impairment of Goodwill	0
Sale of the Institutional Trust and Independent Fiduciary business of ETC	0
Balance at end of period	123,308	114,489	115,276
Investment Management [Member]
Goodwill [Roll Forward]
Balance at beginning of period	46,472	51,185
Foreign Currency Translation and Other	0	(4,713)
Impairment of Goodwill	7,107
Sale of the Institutional Trust and Independent Fiduciary business of ETC	(28,442)
Balance at end of period	$ 10,923	$ 46,472	$ 51,185