Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 30,013us-gaap_ProfitLoss	$ 23,856us-gaap_ProfitLoss
Other comprehensive income (loss):
Change in unrealized gains on securities	883	787
Increase (decrease) in fair value of cash flow hedge	(2,330)	(1,056)
Less: reclassification adjustment for amounts recognized in net income	(956)	(528)
Total other comprehensive income (loss)	(2,403)	(797)
Comprehensive income	27,610	23,059
Less: comprehensive income attributable to noncontrolling interest	(330)	(323)
Comprehensive income attributable to common stockholders	$ 27,280us-gaap_ComprehensiveIncomeNetOfTax	$ 22,736us-gaap_ComprehensiveIncomeNetOfTax

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

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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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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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