Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Nov. 15, 2016	Nov. 10, 2016	Dec. 31, 2015	Nov. 04, 2015	Jul. 14, 2015	Dec. 31, 2014	Dec. 03, 2013	Aug. 30, 2013	Aug. 20, 2010	Aug. 12, 2010
$400 Million Credit Facility \| Secured Debt
Maximum borrowing capacity	$ 400,000	$ 400,000		$ 400,000
$100 Million Term Loan Facility \| Secured Debt
Maximum borrowing capacity		100,000			$ 100,000							$ 100,000
$253 Million Term Loan Facility \| Secured Debt
Maximum borrowing capacity		253,000			253,000						$ 253,000
$44 Million Term Loan Facility \| Secured Debt
Maximum borrowing capacity		44,000			44,000				$ 44,000
$98 Million Credit Facility \| Line of Credit Facility
Maximum borrowing capacity	98,000	98,000	$ 98,000		98,000	$ 98,000
$148 Million Credit Facility \| Line of Credit Facility
Maximum borrowing capacity	$ 148,000	148,000			148,000		$ 148,000	$ 148,000
$22 Million Term Loan Facility \| Secured Debt
Maximum borrowing capacity		$ 22,000			$ 22,000		$ 22,000			$ 22,000