Notes and Bonds Payable - Senior Notes (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 04, 2009	Dec. 13, 2010	Mar. 26, 2013
Debt Instrument [Line Items]
Notes and bonds payable	$ 1,403,692,000	[1]	$ 1,348,459,000	[1]
Senior Notes [Member] | 6.500% Senior Notes Due 2017 [Member]
Debt Instrument [Line Items]
Senior notes face value	300,000,000		300,000,000		300,000,000.0
Unaccreted discount	(692,000)		(992,000)
Notes and bonds payable	299,308,000		299,008,000
Senior Notes [Member] | 5.750% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Senior notes face value	400,000,000		400,000,000			400,000,000.0
Unaccreted discount	(2,136,000)		(2,422,000)
Notes and bonds payable	397,864,000		397,578,000
Senior Notes [Member] | 3.75% Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Senior notes face value	250,000,000		250,000,000				250,000,000.0
Unaccreted discount	(1,747,000)		(1,923,000)				(2,100,000)
Notes and bonds payable	$ 248,253,000		$ 248,077,000

[1] Level 3 - Fair value derived from valuation techniques in which one of more significant inputs or significant value drivers are unobservable.