Derivatives Derivatives - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019
Derivatives designated as cash flow hedges:
Beginning balance	$ 1,282,782	$ 1,240,516
Unrealized (loss) gain recognized in OCI	(17,013)	16,171
Amount reclassified from OCI to earnings	(989)	(1,233)
Net (loss) gain on derivatives (net of tax effect of $6,093 and $5,134)	(18,002)	14,938
Ending balance	1,302,111	1,291,228
Net (loss) gain on derivatives, tax	6,093	5,134
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivatives designated as cash flow hedges:
Beginning balance	(3,124)	(4,113)
Cumulative effect of adoption of new ASU (No. 2018-02)			$ (740)
Ending balance	$ (21,866)	$ 10,825