Fair Value Measurements - Carrying Values and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	$ 8,689	$ 0
Carrying Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	230,498	209,337	$ 193,045
Interest rate caps		0	101
Liabilities carried at historical cost on the consolidated balance sheets
Interest rate swaps		8,683	0
Fair Value \| Level 2
Assets carried at historical cost on the consolidated balance sheets
Investments in debt securities	234,413	209,390	193,045
Interest rate caps		29	101
Liabilities carried at historical cost on the consolidated balance sheets
Interest rate swaps		8,683	0
Credit facilities
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	0	6,044	8,207
Credit facilities \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	0	2,321,585	2,355,948
Credit facilities \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	0	2,329,551	2,324,249
Mortgage loans
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	18,850	9,256	41,718
Mortgage loans \| Carrying Value \| Level 2
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	4,177,516	5,263,994	5,305,911
Mortgage loans \| Fair Value \| Level 2
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	4,195,249	5,265,180	5,194,530
Warehouse loans
Liabilities carried at historical cost on the consolidated balance sheets
Deferred financing costs, net	13,471
Warehouse loans \| Carrying Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	1,500,000	0	114,023
Warehouse loans \| Fair Value \| Level 3
Liabilities carried at historical cost on the consolidated balance sheets
Liabilities carried at historical cost	$ 1,501,248	$ 0	$ 114,023

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

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- Definition

Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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