Credit Facilities (Narrative) (Details) (Line of Credit [Member], USD $) In Thousands, unless otherwise specified	0 Months Ended		3 Months Ended
	Jan. 08, 2014		Mar. 31, 2015 extensions	Jan. 08, 2014
Senior Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 750,000			$ 750,000
Credit facility maturity date	Jan. 08, 2018	[1]
Line of Credit Facility Number of Extension Options			2
Extension option period			6 months
Maximum borrowing capacity under unsecured credit facility			1,050,000
Senior Unsecured Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
Senior Unsecured Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.30%
LHL Unsecured Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility maturity date	Jan. 08, 2018	[2]
Line of Credit Facility Number of Extension Options			2
Extension option period			6 months
Maximum borrowing capacity under unsecured credit facility	$ 25,000			$ 25,000
LHL Unsecured Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
LHL Unsecured Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.30%

[1] Borrowings bear interest at floating rates equal to, at the Company’s option, either (i) LIBOR plus an applicable margin, or (ii) an Adjusted Base Rate plus an applicable margin. As of March 31, 2015, the rate, including the applicable margin, for the Company’s outstanding LIBOR borrowing of $342,000 was 1.88%. There were no borrowings outstanding at December 31, 2014. The Company has the option, pursuant to certain terms and conditions, to extend the maturity date for two six-month extensions.

[2] Borrowings bear interest at floating rates equal to, at LHL’s option, either (i) LIBOR plus an applicable margin, or (ii) an Adjusted Base Rate plus an applicable margin. There were no borrowings outstanding at March 31, 2015 and December 31, 2014. LHL has the option, pursuant to certain terms and conditions, to extend the maturity date for two six-month extensions.