CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
COMPREHENSIVE INCOME	$ 142,164	$ 112,462
LESS: COMPREHENSIVE INCOME ATTRIBUTABLE TO NONCONTROLLING INTERESTS	1,163	575
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	$ 141,001	$ 111,887

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration