Segment Reporting Segment Reporting (Reconciliation of Segment Revenues to Consolidated Revenues) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues	$ 351,224	$ 94,201	$ 335,817	$ 156,811	$ 339,201	$ 107,864	$ 304,868	$ 101,745	$ 938,053	$ 853,678	$ 768,492
Intercompany private sale commission revenues charged by Agency to Principal	309,582	76,229	316,187	123,128	327,592	76,929	294,943	94,175	825,126	793,639	717,231
Agency [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									825,126	794,179	717,231
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									947,058	864,169	776,271
Operating Segments [Member] | Agency [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									825,126	794,179	717,231
Operating Segments [Member] | Principal [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									69,958	30,638	26,180
Operating Segments [Member] | Finance [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									42,018	31,228	25,486
Operating Segments [Member] | Other Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total Agency segment revenues									9,956	8,124	7,374
Segment Reconciling Items [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Intercompany charges from Finance to Agency									(9,005)	(9,951)	(7,779)
Intercompany private sale commission revenues charged by Agency to Principal									$ 0	$ (540)	$ 0