Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	$ 60,198	$ 73,826
Gross Amounts of Recognized Liabilities, Derivative Liabilities	71,586	83,409
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	2	627
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	2	627
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	60,196	73,199
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	71,584	82,782
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Assets	0	0
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	69,545	81,260
Net Amount, Derivative Assets	60,196	73,199
Net Amount, Derivative Liabilities	2,039	1,522
Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	46,260	54,877
Gross Amounts of Recognized Liabilities, Derivative Liabilities	2,155,456	2,205,264
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	46,260	54,877
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	2,155,456	2,205,264
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Assets	0	0
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	0	0
Net Amount, Derivative Assets	46,260	54,877
Net Amount, Derivative Liabilities	2,155,456	2,205,264
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	60,198	73,826
Gross Amounts of Recognized Liabilities, Derivative Liabilities	70,568	81,495
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	2	627
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	2	627
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	60,196	73,199
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	70,566	80,868
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities	69,545	79,912
Net Amount, Derivative Assets	60,196	73,199
Net Amount, Derivative Liabilities	1,021	956
Interest Rate Swap [Member] | Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	2,155,456	2,205,264
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	2,155,456	2,205,264
Net Amount, Derivative Liabilities	2,155,456	2,205,264
Futures Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities			$ 1,348
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities			0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities			0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities			1,348
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities			1,348
Net Amount, Derivative Liabilities			$ 0
Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities, Derivative Liabilities	1,018	566
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,018	566
Net Amount, Derivative Liabilities	1,018	566
Currency Swaps [Member] | Variable Interest Entity [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets, Derivative Assets	46,260	54,877
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0
Gross Amounts Offset in the Consolidated Balance Sheet, Derivative Assets / Liabilities	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	46,260	54,877
Net Amount, Derivative Assets	$ 46,260	$ 54,877