Notes and Bonds Payable - Senior Notes (Details) - USD ($)	Dec. 31, 2015	Apr. 24, 2015	Dec. 31, 2014	Mar. 26, 2013	Dec. 13, 2010
Debt Instrument [Line Items]
Notes and bonds payable	$ 1,431,494,000		$ 1,403,692,000
Senior Notes [Member] | 3.875% Unsecured Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Senior notes face value	250,000,000	$ 250,000,000.0	0
Unaccreted discount	(196,000)	$ (200,000)	0
Notes and bonds payable	249,804,000		0
Senior Notes [Member] | 6.500% Senior Notes Due 2017 [Member]
Debt Instrument [Line Items]
Senior notes face value	0		300,000,000
Unaccreted discount	0		(692,000)
Notes and bonds payable	0		299,308,000
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	(1,832,000)		(2,136,000)
Notes and bonds payable	398,168,000		397,864,000
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	(1,565,000)		(1,747,000)	$ (2,100,000)
Notes and bonds payable	$ 248,435,000		$ 248,253,000