Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Reclassification of other securities to other assets	$ 0	$ 0	$ 3,604	$ 0
Mortgage Loans
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Net gains from fair value changes of mortgage loans	2,076	$ 1,864	4,197	$ 9,470
GNMA
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Mortgage loans previously sold			52,212
Mortgage loans held for sale measured at fair value	$ 0		0		$ 43,035
ASU 2016-01
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Reclassification of other securities to other assets			$ 3,604