Notes and Bonds Payable - Senior Notes (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2013 Senior Notes [Member] 3.75% Senior Notes Due 2023 [Member]	Mar. 26, 2013 Senior Notes [Member] 3.75% Senior Notes Due 2023 [Member]	Dec. 31, 2012 Senior Notes [Member] 3.75% Senior Notes Due 2023 [Member]	Dec. 31, 2013 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 31, 2012 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 13, 2010 Senior Notes [Member] 5.750% Senior Notes Due 2021 [Member]	Dec. 31, 2013 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 31, 2012 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 04, 2009 Senior Notes [Member] 6.500% Senior Notes Due 2017 [Member]	Dec. 31, 2013 Senior Notes [Member] 5.125% Senior Notes Due 2014 [Member]	Dec. 31, 2012 Senior Notes [Member] 5.125% Senior Notes Due 2014 [Member]
Debt Instrument [Line Items]
Senior notes face value					$ 250,000	$ 250,000		$ 400,000	$ 400,000	$ 400,000	$ 300,000	$ 300,000	$ 300,000	$ 0	$ 264,737
Unaccreted discount					(1,923)	(2,100)		(2,422)	(2,693)		(992)	(1,272)		0	(215)
Notes and bonds payable	$ 1,348,459	[1]	$ 1,293,044	[1]	$ 248,077		$ 0	$ 397,578	$ 397,307		$ 299,008	$ 298,728		$ 0	$ 264,522

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