4. Debt Credit Rating for Unsecured Term Loan (Details) - Unsecured Term Loan [Member]	3 Months Ended
	Mar. 31, 2017
London Interbank Offered Rate (LIBOR) [Member] | Moody's, A3 Rating [Member] | Credit Rating Level 1 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.825%
London Interbank Offered Rate (LIBOR) [Member] | Moody's, Baa1 Rating [Member] | Credit Rating Level 2 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.875%
London Interbank Offered Rate (LIBOR) [Member] | Moody's, Baa2 Rating [Member] | Credit Rating Level 3 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.00%
London Interbank Offered Rate (LIBOR) [Member] | Moody's, Baa3 Rating [Member] | Credit Rating Level 4 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
London Interbank Offered Rate (LIBOR) [Member] | Moody's, Baa3 Rating [Member] | Credit Rating Level 5 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.65%
Base Rate [Member] | Moody's, A3 Rating [Member] | Credit Rating Level 1 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Moody's, Baa1 Rating [Member] | Credit Rating Level 2 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Moody's, Baa2 Rating [Member] | Credit Rating Level 3 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Base Rate [Member] | Moody's, Baa3 Rating [Member] | Credit Rating Level 4 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.25%
Base Rate [Member] | Moody's, Baa3 Rating [Member] | Credit Rating Level 5 [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.65%