Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income available to common stockholders	$ 7,409	$ 18,346	$ 35,441	$ 28,228
Other comprehensive income:
Unrealized gain (loss) on derivatives, net of income taxes	5,662	(3,709)	21,833	(4,473)
Less interest income (expense) on derivatives recognized into earnings, net of income taxes	422	(340)	1,636	(904)
Comprehensive income	$ 12,649	$ 14,977	$ 55,638	$ 24,659