Condensed Statements of Comprehensive Income (Parenthetical) (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on interest rate derivative instruments, tax	$ 0	$ (320)	$ 0	$ (511)
Available-for-sale Securities, Income Tax Expense on Change in Unrealized Holding Gain (Loss)	3	0	3	0
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion, Tax	$ 32	$ 15	$ 97	$ 15