Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes Payable	$ 1,294,070	$ 1,292,291
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	9,850	2,150
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(1,913)	(75)	$ (125)
Mortgage servicing rights at lower of amortized cost or fair value			(6,853)
Total gains on assets measured at estimated fair values on a nonrecurring basis	(1,913)	(75)	$ (6,978)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	9,850	2,150
Fair Values
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes Payable	$ 1,303,047	$ 1,285,894