Derivative Instruments - Changes in Other Comprehensive Income Related to Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in other comprehensive income related to derivative instruments classified as cash flow hedges
Balance at beginning of period			$ 939,336
Balance at end of period	$ 1,030,866		1,030,866
Other comprehensive income, tax effect
Reclassifications in earnings, tax	229	$ 21	455	$ 76
Change in fair value of derivative instrument, tax	46	45	208	463
Derivative instruments classified as cash flow hedges
Changes in other comprehensive income related to derivative instruments classified as cash flow hedges
Balance at beginning of period	(3,203)	(3,534)	(3,334)	(2,968)
Reclassifications in earnings, net of tax of $229 and $21 for the three months ended September 30, 2017 and 2016, and $455 and $76 for the nine months ended September 30, 2017 and 2016, respectively	376	35	749	124
Change in fair value of derivative instrument, net of tax of $46 and $45 for the three months ended September 30, 2017 and 2016, and $208 and $463 for the nine months ended September 30, 2017 and 2016, respectively	(75)	(84)	(317)	(739)
Balance at end of period	$ (2,902)	$ (3,583)	$ (2,902)	$ (3,583)