Condensed Financial Information of Registrant (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Cash flows from operating activities:
Net income	$ (2,060)	$ 31,359	$ 40,065	$ 30,496	$ 22,122	$ 28,587	$ 30,517	$ 32,932	$ 99,860	[1]	$ 114,158	[1]	$ 135,586	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Net cash provided by operating activities									191,051		168,073		183,471
Cash flows from investing activities:
Other									(596)		(22)		(649)
Net cash used in investing activities									(271,310)		(150,174)		(130,760)
Cash flows from financing activities:
Proceeds from issuance of common stock under stock incentive plans									3,999		5,510		15,297
Net cash provided by (used in) financing activities									47,004		(66,142)		3,467
(Decrease) increase in cash and cash equivalents									(33,475)		(48,055)		56,222
Cash and cash equivalents at beginning of year				97,126				145,181	97,126		145,181		88,959
Cash and cash equivalents at end of year	63,651				97,126				63,651		97,126		145,181
Parent Company [Member]
Cash flows from operating activities:
Net income									95,405		110,243		131,428
Adjustments to reconcile net income to net cash provided by operating activities:
Equity interest in earnings of subsidiaries									(95,405)		(110,243)		(131,428)
Increase in intercompany receivable									(3,999)		(5,510)		(15,297)
Net cash provided by operating activities									(3,999)		(5,510)		(15,297)
Cash flows from investing activities:
Other									0
Net cash used in investing activities									0
Cash flows from financing activities:
Proceeds from issuance of common stock under stock incentive plans									3,999		5,510		15,297
Net cash provided by (used in) financing activities									3,999		5,510		15,297
(Decrease) increase in cash and cash equivalents									0
Cash and cash equivalents at beginning of year				0				0	0		0		0
Cash and cash equivalents at end of year	$ 0				$ 0				$ 0		$ 0		$ 0

[1] Includes $2.0 million, $1.2 million and $1.1 million for 2011, 2010 and 2009, respectively, related to redeemable and mandatorily redeemable noncontrolling interests.