Equity Change in OCI Recognized in Statement of Operations, Line Item (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gain on sale of investments, net																	$ 376		$ 521		$ 236
Interest Expense, Junior Subordinated Debentures																	2,919		2,427		3,875
Interest Expense, Deposits																	20,884		16,571		16,002
Income tax expense/(benefit)	$ 21,391		$ 8,289		$ 9,963		$ 6,553		$ 7,247		$ 8,652		$ 7,626		$ 7,438		46,196	[2]	30,963	[2]	30,392	[2]
Net income attributable to the Company	$ (18,280)		$ 19,803		$ 23,406		$ 15,662		$ 17,552		$ 19,636		$ 16,398		$ 18,041		40,591		71,628		64,925
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax																	(688)		(979)		(2,354)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gain on sale of investments, net																	376		521		236
Income tax expense/(benefit)																	154		190		97
Net income attributable to the Company																	222		331		139
Hedges related to junior subordinated debt [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense, Junior Subordinated Debentures																	0		0		1,879
Income tax expense/(benefit)																	0		0		804
Net income attributable to the Company																	0		0		(1,075)
Hedges related to deposits [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense, Deposits																	1,179		1,666		2,173
Income tax expense/(benefit)																	491		687		894
Net income attributable to the Company																	$ (688)		$ (979)		$ (1,279)

[1] Due to rounding, the sum of the four quarters may not add to the year to date total.

[2] The Company’s effective tax rate for 2017, 2016, and 2015 is not consistent due to the re-measurement of the deferred tax assets, impairment of goodwill not deductible for tax purposes, earnings from tax-exempt investments, non-deductible compensation, state and local taxes, income tax credits and income attributable to noncontrolling interests having a different impact on the effective tax rate due primarily to the different levels of income before taxes in years 2017, 2016, and 2015. See Part II. Item 8. “Financial Statements and Supplementary Data - Note 17: Income Taxes” for additional details.