CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues:
Investment management fees	$ 530,599	$ 457,538	$ 354,593
Underwriting and distribution fees	532,693	468,057	378,678
Shareholder service fees	131,885	119,290	105,818
Total	1,195,177	1,044,885	839,089
Operating expenses:
Underwriting and distribution	616,031	543,604	449,925
Compensation and related costs (including share-based compensation of $46,473, $40,338 and $30,573, respectively)	161,401	142,255	124,463
General and administrative	80,533	66,703	58,034
Subadvisory fees	29,885	27,823	23,202
Depreciation	15,235	14,030	13,653
Total	903,085	794,415	669,277
Operating income	292,092	250,470	169,812
Investment and other income	2,049	8,737	5,039
Interest expense	(11,413)	(12,723)	(12,695)
Income before provision for income taxes	282,728	246,484	162,156
Provision for income taxes	107,269	89,525	56,651
Net income	$ 175,459	$ 156,959	$ 105,505
Net income per share:
Basic (in dollars per share)	$ 2.05	$ 1.83	$ 1.23
Diluted (in dollars per share)	$ 2.05	$ 1.83	$ 1.23
Weighted average shares outstanding:
Basic (in shares)	85,783	85,618	85,484
Diluted (in shares)	85,793	85,647	85,544